Where's george lets you track currency as it travels around the country.
At this point I've entered about 40 bills totaling about $300. I've been doing this in earnest for about 2 weeks. Granted... at this point, no one has processed my bills.
Basically, when you find currency you enter it into the database by denomination, series and serial number. Preferably you should mark it in someway that denotes that it's being tracked at www.wheresgeorge,com. (This is not illegal. It is only illegal to deface a bill in such a way that it is rendered in a manner that it can not be used or reissued) Then... send it back into the wilds and wait.
If you're looking for instant gratification on this... don't. This can take weeks, months, or even years depending on where the currency winds up and if the person has the inclination to actually take the bill to the internet when they find the bill. So of course, the more people that play... the more likely it is to get a response.
If you decide to play along and register (free) at the site, tell me.. There is a lineage function to see how many bills have been distributed because of you.
I think it's kinda fun.