Because I fear that creditors will somehow infiltrate my bank account, I lean heavily toward a cash world, in my pocket. So I notice stuff. Like all the marks on money.
Given to rumination about objects, I cannot hold a coin, Federal Reserve Note, or vibrator without wondering where it's been.
In my paranoid check-cashing, though, I've noticed an interesting phenomenon on high-value notes. Given that most of our paper currency bears traces of cocaine (esp. here in DC), we shouldn't be surprised that much of our folding money, particularly of high denomination, has gone through the hands of pushers.
And I believe it's druggy folks that use these wonderful little rubber stamps on money. I recently came across a well stamped $100 bill, illustrated here. Who are these people? Is it ego that makes them tattoo our money? Okay, that's a stupid question.
Anyhow, viva "Jhon"!