Three incidents of fake £20 notes in circulation have been reported in the past 24 hours, according to police in north Norfolk.
Residents have been urged to be vigilant after notes were used in shops in Cromer, Felmingham and Stalham.
And retailers are asked to use crime prevention tactics including UV lights or testing pens to establish whether notes are genuine.
PC Pete Davison, north Norfolk engagement officer, said: 'It's concerning to hear of these fake notes being circulated and I would ask people to examine cash carefully.
'If someone tries to offer you any fake notes, or you know any information about those involved in the circulation of counterfeit money, please contact Norfolk Police on 101 or contact CrimeStoppers anonymously on 0800 555111.'
For more information on fake bank notes visit the Bank of England.
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