Church of the SubGenius Propaganda!
If you're unfamiliar with The Church of the SubGenius and you want to change that, they have a website, but all you need to know for purposes of this prank page is that they are a bizarre humor-type cult that appeals to very weird people. (Incidentally, I have been a card-carrying member since 1996.) The above "stickers" are only a small sample of the weirdness that you can spread with their propaganda.
Download two full sheets here:
You can print these onto sticker paper or just regular paper, cut them apart, and put your favorites in unsuspecting places (library books, school lockers, magazines, bathrooms, bus stop benches). If you want larger pieces of propaganda to throw around, the book has some pretty hilarious black and white illustrations that could make good mini-posters.