A 50 Rupee Seychelles note, issued between 1968 and 1973 and features an image of the Queen with the word "sex" secretly written in palm trees is to be sold at Dorchester-based auctioneers Duke’s on October 15.
It has an estimate of £200.
Some believe the word was added because the Seychelles was at the time trying to gain independence from Britain.
It has been suggested that it was done by a rogue engraver, who tweaked the original design of the currency.
There are also those who believe it was just an unfortunate error; however, another note in the series appears to carry the word "scum", implying it was deliberate.
Timothy Medhurst, from the Duke's Auctioneers, said: "This is a very collectable item for obvious reasons.
"Amazingly the added message wasn't noticed - or was perhaps never mentioned - until after it stopped being printed.
"There are various theories about how the word came to be included. Many think the engraver Brian Fox of Bradbury & Wilkinson, the printers, put it in."
Mr Medhurst added: "It is an otherwise attractive note, but would have disappeared into obscurity if it had not been for its secret message.
"I am looking forward to the auction, which will take place on October 15, and said he felt the note would excite collectors.
"Collectors are always keen to have one and this is in good condition and was consigned by a collector.
"It is part of our October sale which will see a huge variety of notes, coins, medals and other related items go under the hammer."
