Red and Yellow cards, and trolls
The Red/Yellow Card project (a way to respond to creepy people at conferences) is a great idea, except for the small problem that trolls might run a scavenger hunt with the object of deliberately getting cards. To reduce the lulz to be had from this, I suggest leaving one of each type of card in the men's room, so that simply holding a card doesn't mean anything.
If you see me at a conference please give me a few cards and I'll help with this. A few men's room users willing to do this would encourage the seeking of lulz elsewhere.