A 1975-dated San Francisco Mint proof dime that does not include the letter S mintmark could bring $500,000 or more at auction. The dime is currently owned by three sisters who grew up on a dairy farm in Ohio; their mother and brother originally purchased the dime 46 years ago for $18,200.

The coin will be publicly displayed at the Great American Coin and Collectibles Show in Tampa, Florida, on September 11-14, 2024. The dime will be sold by GreatCollections in an online auction on October 27.

“The 1975 ‘no S’ proof dime is the world’s most valuable modern coin,” GreatCollections President Ian Russell said. “The sisters, who want to remain anonymous, recently inherited the coin after their mother and brother passed away, and were very excited when I told them the potential value of this long-hidden numismatic treasure. The only other known example of a 1975 no S proof dime sold for $456,000 five years ago.”

The San Francisco Mint produced 2.84 million proof sets – special coins struck with well defined details and reflective surfaces – which were originally sold for $7 apiece in 1975. The sets included six coins with a face value of $1.91 and each one was supposed to bear a letter S mintmark for San Francisco. Only two examples of the 1975 proof dime are known to not have the S mintmark.

The sisters’ dime was kept in a bank vault for over 40 years. It has been authenticated by Professional Coin Grading Service and noted as Proof-67 on the standard numismatic grading scale that goes up to 70.

“The rare no S 1975 San Francisco proof dimes should not be confused with the 585 million dimes struck for circulation at the Philadelphia Mint deliberately without a mintmark that same year. Most of those Philadelphia Mint coins are worth only 10¢ each,” Russell added.

Additional information is available by contacting GreatCollections at (800) 442-6467 or on their website.