What are some different ways I can signal for help in the wilderness?
I'm looking for methods that apply in all seasons, particularly in the mountains, with forests or meadows & plateaus.
It depends a little bit on where you want to signal emergency. But I think you're talking about remote areas. In these areas, searches are most often made by aircrafts. That's why it is necessary that you're seen from above and from far away. So you have a couple of possibilities dependening on your equipement. There is also an Wikipedia article that explains the Alpine distress signal.
Bright clothing: This is especially useful if you're in open terrain and if you don't have any other equipment to signalize an emergency. But with bright clothing it is easier to locate you compared to black/white or grey clothing. So you should enhance your chances and wear yellow, red or orange clothing.
Flashlights: You can use your headlamp or a flashlight to signal the place where you're located. You could for example use the morse alphabet to signal SOS (3 short, 3 long, 3 short) or the international distress signal (6 flashes within a minute, 1 minute pause, 6 flashes within a minute, ...).
Whistles: In the same way you use a flashlight, you can use a whistle. A whistle is a very small and light item, so I would recommend to always take it with you if you're going on a serious trip. The big advantage compared to the flashlight is, that you can hear the sound during daylight or in thick fog, when the flashligts can't be recognized.
Fire: If you have something to make a fire, use it to mark your location. If possible, build a fire triangle. This is also an international distress signal.
Signal rocket: A very useful way to show that you need help. The big advantage is that signal rockets can fly up to 300 or 400 meters so that they are widely visible. The explosion of a signal rocket also leads to an easily recognizable pattern on a radar. The problem is that signal rockets aren't things that are part of a standard euqipment and in some countries it is not so easy to buy one.
Mirrors or other shiny objects: Like flashlights you can use mirrors or other shiny objects to send light flashes. Obviously this works only during daytime.
WHAT ARE YOUR OPTIONS?
You have three main choices:
For any non-trivial situation, I believe the PLB is unambiguously your best option if rescue is your top priority.
THE UNIQUE BENEFITS OF A PLB
PLBs are dedicated rescue devices that hook directly into the military COSPAS/SARSAT satellite rescue system - the same system that would be used by a commercial airliner or ship.
This system was designed specifically for rescue, with global coverage, high reliability, rapid transmission of your message to the base station, and robust response procedures.
The most recent PLB devices transmit your GPS coordinates, which in most conditions will guide rescuers to within 60 yards of your location. The device also emits a local homing signal to guide rescuers directly to you over those last few yards. With a GPS PLB, rescue should be triggered within 5 minutes of activation in North America or Europe. The satellite signal is extremely powerful and should punch through a tree canopy with ease. There are even stories of PLBs working for people buried in earthquake rubble. On activation a PLB should continue to transmit for at least 24 hours, even in severe cold.
PLBs are quality devices that have to meet strict international standards. They use reliable batteries that retain their power for around 7 years as they are not used unless the device is activated. They are pretty compact and weigh around 5oz.
The one disadvantage is that PLBs don't offer messaging so you can't inform the rescue services of your specific situation. So they should only be activated in genuinely life-threatening emergencies when all other options have been exhausted, as a call will trigger a full-scale rescue response.
You register your PLB with the designated authority in your country so rescuers will know about you, your normal activities, and any health issues. There are no ongoing fees.
THE LIMITATIONS OF SATELLITE MESSENGERS
By contrast, satellite messengers such as the Spot and the DeLorme are essentially tracking and texting devices with rescue added as an afterthought.
They hook into the commercial satellite networks Iridium or Globalstar, and use a commercial rescue response centre. These satellite networks are far less robust - just read reviews for satellite phones to understand the issues. And transmission power is around one tenth that of a dedicated PLB so they generally won't work unless you have an unrestricted view of the sky. Because these devices have other draws on the battery such as GPS and messaging their power supply will be much less reliable. And if you do reach a satellite, response may be markedly slower.
Satellite messengers require ongoing contracts which can be expensive and complex to administer. If your account is out of order when you get into trouble you may not be able to use your device. Over their lifetime, they will work out much more costly than a PLB.
These multi-purpose messengers are more suited to casual use and were never meant to be a replacement for a dedicated PLB.
THE LIMITATIONS OF CONVENTIONAL SIGNALLING METHODS
Traditional solutions such as whistles, lights, mirrors or flares offer none of the advantages of either of the satellite-based options. They don't work in storm conditions or if you are remote from other parties, and they offer little help to search and rescue until they are very close to your location.
Personally I always carry a whistle, mirror and strobe, and would use them in frequented areas where there was a good chance of a response before I would resort to triggering the PLB. But they are a very inferior option when things get really nasty.
SEARCH AND RESCUE WILL THANK YOU FOR CARRYING A PLB
As you can imagine, PLBs are very popular with rescuers, who are guided straight to the casualty. Contrast this with resource intensive and often dangerous searches should a rescue be triggered when you fail to reach your destination and your location is unknown. With a PLB, rescue will reach you hours or even days more quickly. Searching large areas for a casualty is a massive exercise, and some people are never found at all...
Do please think of these selfless rescuers (very often volunteers) and make their lives easier by carrying a PLB. In some jurisdictions a PLB may also save you a fortune in rescue charges as there will be no need for extensive search.
IN WILDERNESS COUNTRY, A PLB IS THE WAY TO GO
As someone who does a lot of solo walking in remote locations, a PLB offers considerable peace of mind. My finances are tight, but I regard it as a very worthwhile investment and so does my family.
Over its lifetime a PLB will only cost you around $40 a year. If you go into wilderness country, you owe it to yourself, to your loved ones and to the rescue services to carry one.
In general, anything out of the ordinary can get the attention of a search party or whomever.
During the day, a smoky fire is more visible than a bright one. Build the fire, then add wet material to make smoke.
Be sure to read the Wikipedia article on distress signals.
Before going in to the wilderness, make a plan for how you will deal with an emergency in that setting, including how you will get help.
Use a cell phone.
Use a sat phone if you have one.
Use the methods that Roflcoptr outlined above.
It is generally a good idea to carry some sort of emergency signaling equipment if you go into the wilderness.
Whistle : has limited range but is especially useful if you get separated from your party in fog or snow or if it is likely the peopel will be searching for you on foot. Internationally recognised distress signals are SOS in morse code (... --- ...) or six long blasts every minute.
Mirror : also known as a heliograph. A heliograph mirror is a good candidate for inclusion in a survival kit, these can have very long range in sunlight and are especially useful for signaling aircraft or ships. Mirrors can also be improvised from broken glass or by polishing the bottom of a cooking pot, knife bade etc. Also leaving out any reflective material such as glass from a vehicle or aluminium form an aircraft fuselage can make a survival camp easier to spot from the air.
Signal panels : you can get high visibility panels for signalling aircraft but a lightweight high vis vest is also worth having. In dense forest or broken rocky or icy terrain stringing up brightly coloured cord or tape may also help rescuers to find your location, especially if you are in a snow cave etc which may be hard to see from any distance. A large square panel of fabric with contrasting colours on opposite sides is the most versatile.
Radio beacon/sat phone : worth considering if you are going somewhere really remote but maybe a bit expensive for the casual user. These either work or they don't. Obviously you need to know how to use and maintain them and select a type suitable for your application.
Fire : the light of a fire will be visible at night and smoke will be visible by day. The most effective practice is to keep a small fire going at all times and have 3 large signal fires ready to be lit if you notice signs of search nearby. 3 fires make it much more clear that you are making an emergency signal. These should be prepared such that they can be lit and get established quickly and kept dry. During daylight add green wood, grass, leaves, oil or tyres to and established fire create smoke. It may also be worth considering carrying a very reliable fire lighting kit for one or two uses in an emergency in addition to your normal kit. Smoke from fires can also assist aircraft in assessing wind conditions for landing, winching etc but obviously once you've been spotted don't over do it to the extent that the smoke becomes a hazard to rescuers.
Torch : flashing a torch can be a effective signal at night. If you have limited batteries flashing at regular intervals will give you more life out of it than just leaving it on and will be more noticeable as a signal. As soon as you find yourself in trouble you should reserve your torch for signalling or other dire need. Also a strobe light (especially coloured) is a clearer signal and will last longer than a conventional torch.
Writing : you can write a message in snow or sand simply by kicking up a path alternatively use any material you can find (eg grass, branches, wreckage) to write with. There are a variety of internationally recognised ground to air signals. If you only remember one a large X means 'I need (medical) assistance'.
See the question and answers in What order of response time can I expect if I hit the "911" button on my SPOT Satellite Personal Tracker?
We've scorned such wimpy behavior (carrying a satellite personal tracker) for years, until a good friend gave us one, and insisted that we carry it. We've never had to use the emergency feature, but after each trip, we enjoy looking at the messages we've sent home tracking our route.
It doesn't weigh much.
Of course, having people leap into a helicopter to look for you isn't enough. You must stand out from the background. The answers above cover that, except for one thing, which is mentioned in my question in the link above. If you have deliberately camped to maximize your privacy (as the people did in the anecdote cited in the link), a helicopter can spend several hours looking for you. There is a lot of ground down there, from a helicopter's point of view, even when it is narrowed down by the tracker's coordinates. If you are injured, and in pain, you may be delerious (sp ??) or unconscious by the time the 'copter or search party arrives. Set up something artificial-looking while you still can.