altering the design of ancient coins or making
photocopies of bills with high-tech machines,
counterfeiters have made illegal money
the other hand try to protect themselves by
testing and identify counterfeit bills in any
I have seen two
different methods of identifying counterfeit bills. In a
bank I noticed that the cashier holds the bill under a
purple light. In a supermarket I saw the cashier puts a
check mark on the bill using a special marker or pen.
But, how do these
methods work? How can a bank clerk pass the bill under a
purple light and quickly determine if it is a valid
bill. What does the marker do?