Words printed on the small sticker that the American government gives out to people who fulfill their civic duty on Election Day, or during the primary elections. The idea is probably to advertise the fact that other people still have the chance to vote, in case they'd forgotten... although maybe the sticker is supposed to be some kind of reward to those who vote. When I actually see someone wearing a sticker reading "I Voted", the voice in my head reads it with kind of a cartoony squirrel voice, and I lose significant amounts of respect for him or her.