Shop-keepers have been urged to be on the lookout for counterfeit money after a customer used fake notes to buy fast food in Parramatta.
Police said two sham $50 notes were used in two separate transactions at a fast food restaurant on Victoria Road on Sunday.
The outlet's workers noticed one of the notes when they were doing the accounts at the end of the day and a bank teller noticed the second one.
Parramatta local area command crime manager Detective Inspector Stephen Yapp said it was uncommon for counterfeit notes to be discovered the area but when some were found in circulation there were likely to be others.
"Shop keepers should be cautious, particularly with $50 notes at this stage," Detective Inspector Yapp said.
"If people find counterfeit notes they should call the police and officers will obviously investigate the matter."
Shops and restaurants are most likely to be targeted when they are at their busiest.
"When businesses are busy they are often turning over transactions quickly, so it would be more likely that a person with these notes would try to pass them through in the hope they won't be noticed by staff," he said.
Australia has one of the lowest rates of counterfeiting in the world and all Australian bank notes have similar security features.
If shop-keepers suspect a bank note might be counterfeit they should check that the white image printed on the clear window can't be rubbed off, that the note is made of plastic and that the Coat of Arms is visible when the note is held to the light.
Diamond-shaped patterns are printed inside a circle on both sides of the bank note.
If the note is held up to the light, the patterns should line up perfectly to form a seven-pointed star.
Detective Inspector Yapp said fake $50 notes are more common than $100 notes, which draw attention.
Police investigations into the fake notes used on Victoria Road are continuing and security footage is being reviewed.