Marked bill. Marking bills are a technique used by police to trace and identify money used in illegal activities. The serial numbers of the bills are recorded, and sometimes markings are made on the bank notes themselves (such as with a highlighter or other writing ).
In movies (at least) you hear bank robbers demand unmarked bills. They want the money to not be tracable. They would look over the money that was handed to them, to make sure that the serial numbers are not sequential. Unmarked bills are bills that do not fit the definition of marked bills
by No Cuffin June 28, 2014