Do they really mark bills paid in a ransom?

Whenever there’s a ransoming in the movies, the kidnappers always specify that the ransom be paid in small, unmarked bills. Is this a Hollywood invention, or would they actually mark bills in real life? How would they mark them exactly, would you be able to tell if someone were to pay you with a marked bill? Wouldn’t they just track the bills by the serial number anyway?

There are many inks that are invisible until illuminated with UV light.

An easy way to mark the bills would be to collect them into a stack and make one or more stripes across the edges of the bills with invisible ink.

No, the easiest way to “mark” bills is to just write down their serial numbers.

This is how most banks do it – there are bills in the bottom of each cash drawer that are not used for making change, but their serial numbers are written down. If stolen, the bills can be identified.

Funny, I can’t image tellers spending time tabulating bill serial bill serial numbers. In fact, even in pre-machine automation day of banks, (i dunno, pre 1970?) this just seem like a task teller did (seems too time consuming).

It would be easier for a wad of new bills, where the serial number would be consecutive (which is in turn, why the bad guys demand used bills)

It’s called “bait money”. In all of the setups I’ve seen the bait money is kept in an otherwise unused compartment of the cash drawer. They are most often used in conjunction with a silent alarm. The edge of one of the bills is slid between two contacts while the others are stacked on top, hiding the alarm contacts. Looking into the cash drawer reveals nothing unusual. When the bills are pulled (specifically the botttom bill) the contacts engage and an alarm is sent. Bait money is made up of real bills so that the thief has no way to know anything is amiss.

There is usually one bait money setup for each teller or teller station. The serial number on each bait money bill is recorded and a list, by teller or station, and kept at the branch. Each list is audited regularly to ensure accuracy. If the thief is caught with the cash, police will obtain the bait money list for the robbed teller(s) and match it to the cash recovered.

But where is the payoff? Are banks or law enforcement going to go through millions of bills transacted every day to scan for the recorded numbers?

The logistics of this seem impracticable.

If they catch you, and you have the bills, then they’ve proven most of their case.

I’ve never understood this myself, but here is a famous example:

Lindbergh kidnapping (serials on gold certificates)

From the above link, I found this informative:

Actually, a slightly easier way to “mark” bills may be just to photocopy the side of them with the serial numbers.

Frequently in the buy and bust cases I sometimes have to read the court notes that the detective either wrote down of the serial numbers of the bills used for the buy and found on the arrestee, or notes that the bills were photocopied and the serial numbers compared.

That’s how Cleveland PD narcotics detectives do it in so-called “controlled buys.” After the drug purchase is made by undercover detectives or an informant, uniformed cops swoop in and nab the dealer, who still has the bills with the previously-recorded serial numbers on them.