Keeping track of your money

I made a purchase at a convenience store this afternoon and two of the bills I received in change were stamped as being registered at Where's George?, a currency tracking project. I entered the bills at the website and learned they'd started at Omaha, Nebraska, in January 2009.

Where's George? started in 1998 and has spawned other tracking projects. I could buy a rubber stamp or two to mark bills myself but I don't see that happening any time soon. The Christmas present for someone hard to buy for, perhaps? The bills I received today had a total of six different stamps on them!