Police in Strabane have warned that counterfeit banknotes have been found in circulation there.
Traders and business people have been advised to check that each note they receive is genuine.
A police spokesperson said that there are a number of ways of telling if a note is authentic.
Notes that look or feel different or that are faded should always be double-checked.
The colours should be clear and the print on the banknote should be distinct and well-defined.
The banknote should feel crisp and not be limp, waxy or shiny.
The watermark is a very important security feature and should only be visible when the note is held up to the light.