Leave easily mistaken receptacles around for people to accidentally deposit specific items in for you, or others, to collect later.
(I might have done this by accident today: I picked up my coat from the work hatstand, to later find a pound coin in there which I don't think belonged to me. If it wasn't mine, someone must've put it in there assuming they'd got their pocket, when in fact they got mine.)
Obviously you could use this technique to be mean, or you could use it to exact some sort of vigilante justice on very specific target audiences, or just to generally snicker about being subversive.
You could also imagine a social game version of it, whereby people notice said masquerade receptacles around the place and deliberately fulfil them, as a sort of push-pull version of the traditionally push-only generosity game.
Perhaps I prefer that variety: a sort of hidden cache game whereby people who know the game and the specific signals can pick up free bonuses, and give them out :)-- conskeptical, May 16 2007 the generosity game http://www.generosity.org/spread random acts of kindness [conskeptical, May 16 2007] http://www.geocaching.com/ A sort of hidden cache game [jutta, May 16 2007] I'm not sure I understand this thing in its exactitude, but the general concept sounds much like something I would like.-- wagster, May 16 2007 sounds pervy.-- po, May 16 2007 You mean like putting a fake post box (US mail box) in the street so people give you their letters?-- marklar, May 17 2007 [marklar] - that would count, although it seems probably a little too vindictive for my style :)-- conskeptical, May 17 2007 Occasionally my dryer leaves quarters in my pockets :P-- evilpenguin, May 17 2007 random, halfbakery