canyonwren mentioned Where's George in her journal before, and I just got a marked bill today in change at lunch. (The waiter came back with my change, and I was planning to leave the ones as a tip, but I spied the URL on one of the bills, so I had to swap out the cool $1 with a virgin bill from my wallet. I'm sure that if anybody was looking, they'd be convinced that I'm insane or an idiot.)
I proceeded to register all the money in my pocket. I encourage you to do the same.
Oh, you've probably got here because you still have no idea what I'm talking about. Where's George is a database that you enter in "spottings" of US paper currency - typically one dollar bills for obvious reasons. It's more fun than a chain letter, but it has a little bit of the same frisson of excitement when you discover that a bill in your hand has been in Gresham Oregon. Or somewhere more exciting. Or that a bill that you spent has made it across the country.
The bill that I got had, in friendly (female?) print on the margin www.wheresgeorge.com, which was all I needed to finally get around to logging in.
My quandary now is whether to mark all my bills (probably not illegal) or not. If I do mark all my bills, then the next time I pay for something with a handful of marked cash, I'll have a hard time pulling off the "Oh, I got the bill that way" lie. And if I don't mark the bills, I'm very unlikely to get any hits.