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This stack of fresh bank notes, with serial numbers in complete sequence
(lemmy.blahaj.zone)
None in the middle are missing.
Requesting to be paid in nonsequential bills is something only a criminal would do, so the joke is that the purchase is illegal.
The idea is that if the person paying you is a cop, they'd give you bills they can track down later. I'm not sure if that's actually done in real life. Apparently a large percentage of printed cash is used for illegal deals, so I dont think criminals are too concerned about being traced by their cash transactions.
It's easier for the media to say "the criminal was paid in bills with the serial numbers B12340000 to B12349999" than list 9999 different serial numbers for tellers to be on three lookout for.