It doesn't have to be one of the high class glass mirrors either, altho they are much better. I have signled more than one chopper in with an old "tin" mirror I always kept in my pinch book, It did have a hole that I drilled in it. It never failed to amaze me how difficult it can be for a chopper to spot you in some terrain, even if you have radio contact, but they never failed to spot the flash...