When I was in college, I got to thinking about paper money, and how we typically spend paper money in the same places, ie. the same fast food restaurants, the same convenience stores, the same gas stations, etc. I wondered how many times I'd held the same $20 bill throughout the course of my life.
I'm fully aware that this is a weed-smoking kind of question, and while I have no problem with weed, I swear to you that I wasn't high at the time.
However, being of a scientific bend, I figured out a way to test this. Whenever I get paid, I like to withdraw money in $20 denominations. Back then, I decided that every bill that I intended to spend would be marked. I put my initials, JB, plus a number (I think I got up into the twenties) on each bill. And then I sent them back into circulation.
This was before I knew what Where's George is. Not that it matters much. Where's George is kind of a hassle, and it's not very conducive to my particular experiment. Although I have participated in that a few times, just to help someone else's experiment.
It's been about fourteen years since I sent my marked bills out into the wild, and to this very day, I have not gotten one back. I thought I might have by now, since so much money is spent locally, but I never did. Maybe someday.
If one day, I get a $20 that says JB15, or whatever number, I think that would be amazing. But by now, I have given up hope. If anyone ever gets one, please let me know.