No Space? Leave the Place!
Two Way Mirror Test shared by a Facebook friend ...
Do you know how to determine if a mirror is 2-way or not?
Just conduct this simple test: Place the tip of your fingernail against the reflective surface and if there is a GAP between your fingernail and the image of the nail, then it is GENUINE mirror. However, if your fingernail DIRECTLY TOUCHES the image of your nail, then BEWARE! IT IS A 2-WAY MIRROR!
"No Space, Leave the Place" So remember, every time you see a mirror in a public place, do the "fingernail test." It doesn't cost you anything.
Post Update: Looks like this not quite be all that accurate for all mirrors. Check out the Snopes article for more info.