system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do criminals in movies always ask for unmarked bills. What is the difference between marked and unmarked?
gpt
"Marked" bills have had subtle distinctive markings added, or their serial numbers have been recorded, as an anti-theft measure.  These bills were never intended to be handed out to customers; they're something for thieves to take so that the police can identify them if they're found in possession of the marked money later on.  

"Unmarked" currency is just regular cash.