Here's a clever ad that UNICEF put out a few years ago to raise funds for people who have been maimed by landmines. Stickers, camouflaged to look like pavement, were left on sidewalks. When someone steps on one, it sticks to the bottom of his/her shoe. The underside informs the victim that if it had been a landmine, s/he would have been mutilated.
Link via Everyday, No Days Off | Image: Leo Burnett