A Perth-based TikToker and currency expert has revealed the tiny detail on a rare 20c coin that can see it fetch eye-watering prices of up to $4,000.
Joel Kandiah, whose video has garnered more than 46,000 views, has urged Aussies to 'empty out (their) coin jars' and check for one of the special coins.
According to Mr Kandiah, who goes by @thehistoryofmoney on TikTok, the coin can be worth between $250 and $4,000 - a staggering 20,000 times its nominal value.
'Find a 20c coin from 1966 and turn it over to the tails side,' Mr Kandiah said.
'Look at the bottom of the number two - at the top of the base, if it's wavy, you're gonna be in the money.'
Around half of the Australian 20c coins made in 1966 were struck by the Royal Mint in London where one of the tails dies used was damaged and touched up, resulting in the distinctive 'wave' pattern on the number two.
The 1996 wavy baseline 20c is still the most sought-after rare Australian 20c coin.
The coins are still in circulation, with one person commenting on the TikTok that they had three of the rare coins.
Mr Kandiah also pointed out that cleaning a rare coin could lessen its value to a collector.
Collectors are often willing to pay thousands of dollars more than the nominal value of a banknote or coin depending on factors such as its date and condition.
The Australian 20c coin was first introduced with decimal currency in 1966, with Stuart Devlin's platypus design remaining unchanged until 1995.
It replaced the florin, a coin worth two shillings or a tenth of a pound.
The platypus continues to be the standard design for the reverse face except for commemorative designs, while four different obverse face designs have featured on the coin.
Queen Elizabeth II, Raphael Maklouf (a British sculptor) and Jody Clark (a British engraver employed at the Royal Mint whose portrait of the Queen featured on Australian dollar coins) have all featured on the 20c coin.