A fast-spreading "urban myth" has Christchurch residents accusing each other of using counterfeit money and illegally damaging banknotes, the Reserve Bank warned on Saturday.
"People are being told that you can tell a fake banknote by scraping it with a coin, and if the printing comes off revealing the plastic then it's a fake," spokesperson Peter Northcote said.
"This is completely false, not one of our recommended ways to check a banknote, and actually illegal defacement."
He said occasionally notes will lose some of their printing - particularly if they've been folded.
"This fake test actually highlights one of the security strengths of our banknotes, being the polymer base they’re printed on.
"A genuine banknote won't tear from the edge, whereas almost all fakes will as these are usually made with ordinary paper and feel different in the hand.
"Other simple checks are for sharp printing, an intact embossed window, and the rolling sparkle on the small bird in the corner of notes with the large window."
Northcote said damaged banknotes are withdrawn from circulation "when they pass through the cash handling machines working for banks and major retailers".
Guides on how to spot a real fake is on the Reserve Bank's website.
The bank has previously said only about four in a million notes are fake, "low levels of counterfeiting by international standards".