I watched A Simple Plan (1998) at the weekend and SPOILER ALERT: a large percentage of the bill's serials were recorded.

I just don't understand in practice how this is an issue.

Say you spend $100 on groceries with marked cash, how are you de-anonymised? The cash mixes in with all the rest of the cash from other registers and then gets picked up by Securicor and so on.

Never made sense to me!

If you just spent a few bucks on groceries once, then you are in the clear. But if you get doing it repeatedly, or worse, spent a whole bunch of cash to buy a car or something expensive, then when that money did get back to a bank then eventually those numbers will be identified and FBI will be notified. If you are trying to spend $20 or $100 in marked bills, you'd be fine. But try that with 4 million in $100 bills, it won't take long for them to find you. Not instantly, but eventually.

I'm assuming you're wrote this tongue in cheek. Cooper absconded with his bills in 1971 — 54 years ago. Do you really believe that spending one of them today would bring trouble?

I think there'd be a fair amount of interest though I'm not sure how tightly bills returned for destruction are monitored for known serial numbers like that so I'm not sure if anyone could notice. But if they are I think it'd trigger some interest at least just to figure out where you might have gotten it from.

Anyone know if there's a monitoring program for serial numbers of interest?

51.years.ago.

It's just numbers in a database if they're doing automated scanning, it's basically free to keep an alert around, and if the bills show up new out of nowhere it means there's a decent chance you're relatively close to their original source.

The FBI gets out of bed for more inane things than maybe figuring out what happened to DB Cooper (he probably died during the jump or after landing) after all this time.

I should have wrote "will draw attention" rather than "you'll get into trouble". I also mistakenly thought there were already pre-photographed ransom bags by that time, those came later.

These arguments suppose there's an FBI agent with a printed list of serial numbers positioned nationwide at every store.

In practice, if you spend less than $10,000 a time, you'd probably be fine?

They have the list on computers now.

Well, yes you are correct. Physical bills have unique serial numbers and a small (effectively insignificant) percentage of these bills are flagged as stolen and can be seized.