How great are your odds of getting the same bill back that you had used for a purchase say several weeks before? Are your odds greater with a larger bill or smaller bill? I would imagine that marking bills to track them would be against the law, but it might be interesting to see a bill come back to you several weeks later in change.
It’s only against the law to deface currency with intent to render it unfit to be reissued:
Scribbling your name or a date on the bill doesn’t render it unfit - you’ve probably gotten many bills with various things scrawled on them, many by people performing exactly the experiment you’re suggesting. I don’t think drawing beards and moustaches on George Washington qualifies either.
Here’s a website you might be interested in:
I suspect you are much more likely to get a bill back if you live in a smaller place - their data suggests that most bills circulate around locally in between occasional large leaps, which makes sense.
Dammit, dammit, dammit!
yabob beat me to it! I actually got one of the bills in the Where’s George? program. It was a five that started out in Northern Maine and ended up a year and a half later in loer Westchester County, NY. It was stamped in green ink with the website address.
If only I could type faster…
i used to regularly mark my notes as a kid ( with my name ), mostly small currency… not one of 'em ever came back… but that’s not surprising in a country of 1 billion…