www.wheresgeorge.com
is a fun site I don't remember to use often enough.
With the advent of the internet, it's possible to track your paper bills as they wander the globe. Many people are doing just that, logging into this site and entering their bills' numbers, leaving notes for each other about where they found bills and what condition they were in. You may never reach that out-of-the-way spot, but your money might -- and now that money can talk!
It's illegal to deface money in a way that renders it "unfit to be used," but it's not illegal to mark it -- or bank employees counting stacks would get in big trouble. So Where's George?® users usually write the URL of the website (and perhaps a "track me!" or other brief note) on their bills and enter them into the website before sending them out into the world. Entering them first is important - Where's George?® can't start tracking until it's got a starting point.
Schools have used Where's George?® to teach, and scientists are using Where's George?® data to help them model how diseases spread.
Some people -- like me -- just mark bills every now and then; there are some Where's George?® users who make a game of it, trying to "hit" all fifty states or as many countries as possible or all the counties in their states. Some have created little utilities to add an automatic visual tracking map for each of your registered bills.
At the moment, Where's George?® tracks all denominations from $1 to $100 (paper only), and there's a companion site called Where's Willy?® for Canadian money.