The 1975-S Proof Set with no mint mark on the dime is an interesting variety that has caught the attention of coin collectors. Proof sets are specially made by the U.S.
Mint for collectors and typically include proof versions of circulating coins from that year.
In the case of the 1975-S Proof Set, the absence of a mint mark on the dime is considered an error. The "S" mint mark indicates that the coin was struck at the San Francisco Mint.
However, for some reason, a small number of dimes in the 1975-S Proof Sets were struck without the mint mark.
Coin errors like this can occur due to various reasons, such as worn dies, improper maintenance of minting equipment, or other anomalies during the minting process.
While some errors are caught and corrected before coins are released into circulation, others make it past quality control and end up in the hands of collectors.
Because of their rarity and uniqueness, error coins like the 1975-S Proof Set dime without a mint mark can attract significant interest from collectors.
They serve as reminders of America's founding principles, values, and achievements, making them cherished artifacts for generations to come.