I asserted that there was no technological or cost issue at this point associated with OCR'ing serial numbers on inbound deposited cash outside of an envelope, never mind _outbound_ cash. So even a self-replenishing machine should be able to associate notes with individuals appearing on the camera at the ATM. Which seems, from a law enforcement perspective, kind of useful.
R. was skeptical, but it turns out that there have been desktop money counters with serial number capture since around 2011 -- and a bunch of ATMs now have that retrofitted into them. In the course of figuring this out, I ran across some forums discussing whether or not money was ever tracked by serial number (excluding things like bait money in a teller drawer). People popped up with an Enid Blyton story, Dorothy Sayers, and someone said their wife used to work at a school where they logged all cash by serial number.
So I sat back, and thought, well, if you look at inflation in the US, a $20 bill through when I was born was _definitely_ worth tracking -- in today's money, more than a hundred dollars. I'm betting a lot of institutions tracked serial numbers on some or all of their cash (the petty cash drawer seems like a great candidate, since there is so little security on it, and you really don't want people thinking they can just dip into that at will) until the inflation of the 1970s made it just a Pain in the Ass, at which point they quit and we all never knew they were doing that except for things like schools that hung onto the practice by switching to photocopying in the late 1970s or early 1980s.
It is sort of interesting to realize that everyone who is avoiding loyalty cards and credit cards and other instances of the Number Of the Beast are now going to have to start worrying about the serial numbers on the folding green stuff. Because in a few years, we're going to be able to track all those bills moving from business to bank and bank to individual and individual to business and so forth.
Ah, who am I kidding. I'm sure the paranoid folks out there have been worrying about this for a while, and that's why they want to go back to gold. Or something. [ETA: Yup. Barcodes on currency. Something about Donald Regan and John Kerry and currency recall and blah blah bleeping blah.]