small, unmarked bills

Noun

 * 1)  Paper currency which consists of small-denomination banknotes that have not been inscribed with hidden markings which would help authorities identify and trace them.

Usage notes

 * Often used to refer to the money demanded by a bank robber, extortionist, or kidnapper.
 * Also used, by extension and sometimes humorously, to refer to readily spendable cash obtained by any illicit or somewhat questionable means.