"I Voted" stickers are traditionally handed out after a person votes in an election. During the 2008 presidential election, several food establishments were giving out free election day food if customers used their "I Voted" sticker as 'proof' of having voted.International Business Times: 'I Voted' Stickers Gets You Free Ben and Jerry's ... (November 4, 2008)
Krispy Kreme, Ben and Jerry's and Starbucks were among the food chains honoring "I Voted" stickers in exchange for free food. The Atlanta Journal-Constitution reported that the Georgia Secretary of State office warned that the practice may violate election laws.Ajc.com: State Says Voter Freebies Against the Law (November 4, 2008)