A modern (Korean War era and later, at least) signal mirror has not just a hole in the center but the hole is surrounded by a grid of retroreflectors. You aim the mirror spot at something close by, then look through the hole. The grid makes a very bright spot in your vision where the mirror's reflection is going. You then simply tilt and rotate the mirror to put that spot on your target.
There is no need to put a dot of light on your cheek or on a nearby rock or anything else, unless the sun-to-mirror-to-target bounce makes a very shallow angle, say more than about 135 degrees. In that case the retroreflecting grid doesn't work and you have to use other methods.
Image ganked from this flickr page. As it says there, several companies do make "signal mirrors" that appear to have a grid around the hole, but don't actually have retroreflectors and don't make the bright spot. If you buy a US signal mirror on eBay and it says "Mark III", it's the right thing.