John Scalzi on his Whatever blog asks for comments to an entry on his blog from anyone and everyone, just saying that they voted. It just says "I've voted today. Presuming you're eligible to vote in the US, let me know when you have, too." It's not about who voted for whom, just the fact that you cast a ballot. So far he's had 143 voters stop by.
Huh, I wish I had seen this in a timely fashion. I really wish they gave out those stickers in New York.