This might be off-topic so I understand if this gets closed.

I'd like to set up a kind of treasure hunt (perhaps geocaching) for my friends. I was thinking that I could take pictures of places (signs, doors, corners of buildings, stuff like that) but from quite close so that you won't see the surroundings to make it a bit harder, and hide something (text, a hint) to where the picture was taken.

An example: A picture of a graffiti from under a bridge (the picture shows only the graffiti). My friends, once they find out where the graffiti is, go to the bridge and find the next hint.

The problem is how to place the hint (probably text) to the place I want so that it stays there. If I'd leave a post-it note, there's a chance someone will take it if they see it. If I write with a marker on a wall, it'd probably stay there, but I'd rather not do any "permanent" damage to buildings and structures.

Any ideas how to accomplish this? How to hide text on public so that it stays there and without damaging property?

  • 1
    A passing thought: rely on a combination of a text that already exists either in situ or on the map, combined with a clue in a geocache or on a clue sheet. Neither needs to be useful without the other.
    – Chris H
    Mar 19, 2016 at 18:27
  • 1
    How about chalk?
    – flawr
    Mar 19, 2016 at 23:13
  • 2
    It seems your question is how to make a durable or permanent modification to a site without having such a modification be durable or permanent. If your question was more about how to use an existing site to direct someone to the next clue you might have more luck; Chris' suggestion is certainly on the right track.
    – requiem
    Mar 20, 2016 at 19:12

4 Answers 4


Augmented Reality...

... is what you are looking for.

I basically agree with Olin Lathrop's answer:

You don't, or at least shouldn't. As you say, it's public property, not yours. What you are asking is no different from how to leave garbage around your campsite so that casual observers won't see it. It's just plain irresponsible, and probably illegal.

But there is something you can do about it. You may want to use "Augmented Reality". It's really easy: just download an app like for example WallaMe or Augment and set up your hints. Share them with your friends and thus make them visible when they (your friends) hover over the places with their phone's cam.

The description from Google Play:

Hide messages in the real world using augmented reality.

Leave a message on the wall, or somewhere in a real place, that can be seen only by those you want. It's a funny way to hide private messages in public places.

Take a picture of a wall near you, add pictures or freehand sketches and share your creation with your friends. Your augmented reality wall can then be viewed by your friends when they are in the location where you created it. You can also make your wall public, so everyone passing by the physical location can use the WallaMe unique viewer to see your augmented reality Wall.

WallaMe makes creating your own virtual reality easy - be creative with beautiful stencils, freehand drawing tools, geolocation and image sharing features.

Enjoy the live image stream of public walls being created worldwide within the WallaMe app.


There are even a few geocaches (quoted example) which use this technology:

Augmented reality (AR) is not all that new but it has become more popular with the proliferation of mobile devices such as phones and tablet/pads. I was first exposed to it by my son who was playing a game on his Gameboy. The game came with marker cards that made 3D characters from the game appear in the air hovering over the card. Now, AR lets you use your mobile device to see things that are not really there. There are apps that let you use your smart phone or tablet to scan your surroundings and show photo links, advertisements, directions, etc. It is like a cool, secret world that only folks "in the know" can discover.

AR works by using some kind of tag or marker. That marker tells your mobile device to display the predetermined image or information at that spot. Markers can be something like the printed card in this geocache listing, a logo or photograph, or they can even be a physical GPS coordinate- meaning that if you stand in a certain spot and use some AR apps you will see the hidden information.

If you want more information about AR look up Wikitude or Google Project Glasses.

Click the following link and print the special marker page image. This sheet is the key to it all and makes the magic happen. It is the same jpg included in the gallery of this cache listing. Place it on a horizontal, well lit surface in front of you.

Now all you need to do is to obtain a free AR app called Augment. It is available for Android and iPhone users. The first time you run the app it takes you directly to the camera. Please hit your BACK button or navigate to the home screen of the app. Then touch the logo in the top left corner of your screen in order to expand a menu from the left side. (That is how it works on my Droid. iPhone users may have to do something different). Choose SCAN. This will active your device's camera so you can point it at the USCGA logo shown below. You don't have to print the logo. You can just use the camera pointed at the screen.

This information is quite important for "Augment" because it works you around printing the "data cards":

NOTE-- Some cachers have figured out how to do the AR portion of this cache puzzle using two phones instead of printing the marker sheet. They use one device to display the marker and the other device to do the scanning. (...)

Voilà an easy, beautiful and leave-no-trace solution - have fun :)

  • 3
    Oh that's really cool, I've never thought something like that existed at all +1
    – Kyle
    Mar 21, 2016 at 17:32

Use something that is already there.

I competed on a similar event recently - a set of clues were given out that each led to a location, and at each location the clue gave a number (for example, "how many bolts on the gate", or "What's the third digit of the sign-makers phone number") - these numbers together gave a map reference to the next control location, where another set of clues were handed out for the next part of the event.

This way you don't deface anything, and you can be sure that the clue you find when you're setting the event will still be there when your friends go looking (as long as you use something permanent, like my above examples of gates and signs - graffiti would be a bad idea as it might get cleaned up in the mean time)


You don't, or at least shouldn't. As you say, it's public property, not yours. What you are asking is no different from how to leave garbage around your campsite so that casual observers won't see it. It's just plain irresponsible, and probably illegal.

A good test is what would happen if lots of people did the same thing you are considering. Picking one flower or making one chalk mark isn't a big deal. But we can't have 100s of people doing that, so the only way to be fair is to say nobody gets to do it.

Unless you own the land or have explicit permission from the land owner, don't do it.

I do trail maintenance work around town regularly (with permission of the land owners, which includes the public authority on public lands). I sometimes see little markers and the like on trees, and always make a point in removing them. They don't belong there. People do not have the right to put up their own markers and otherwise deface public property. Public property doesn't mean you get to do what you want. It's basically shared ownership with lots of other people, many of whom might object to what you are trying to do. That's why we create authorities to manage and make rules about what is allowed on public property. You can't set up your lawn chair and have a beer in the middle of a public road intersection either, for example.


I had permission to a bunch of adjacent farm/pasture/bush land near a school I worked at. I think this would be reasonable also in utility type public land: community pasture, national forest, wilderness areas, but not in lands whose function is beauty such as parks, or sites that get large traffic flows.

We had an orienteering game that ran in winter. Because it was in winter, I had to have all the controls set up before snow fall. Because I had to adjust the spread of the game depending on how deep the snow was, I needed 3 times as many controls as I expected to use. Because kids were in the school for 3-5 years I had to be able to go that long without reusing a control point.

What I did was to make controls out of 4" squares of UV resistant coreplast. These were affixed to a tree or fence post with a roofing nail, on the north side. I wrote on the squares with an artline 400 paint pen, AND a laser printed Avery weatherproof label.

Each square had an ID and a codeword. E.g. ID A21 Codeword Rambunctious Rhino.

Directions as to how to get there referred only to the ID. Return with the codeword proved that they had been there.

Clues generally had two components: Part one got you to the general vicinity. Part two told you what to look for. So a simple one would be 721 654 using the standard UTM grid. That is accurate to 100 meters. Part 2 would be something like: "Double trunk birch near hill top" More complex ones could depend on plotting bearings from landmarks, figuring out how to do some form of search, doing research on the internet.

If you were making a game for one use, you could skip the nails, and use baling twine. Or you could just write on flagging tape.

At the end of 5 years I had over a thousand controls, spread out over 200 km2 of territory, all with gps coordinates to within 5 meters. In the fall I would take a map of a zone, usually a square mile, and would spend the day checking previous controls and adding new ones if I was inspired to some clever new clue.

The school is not open any more. But a description of the game, and how it works is here:


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