The 1975-S Proof Set is a collection of proof coins issued by the United States Mint in 1975.
Proof sets are specially made for collectors and feature coins struck using highly polished dies and specially prepared planchets to create coins with exceptionally sharp details and mirror-like surfaces.
Regarding the absence of a mint mark on the dime in the 1975-S Proof Set, it's important to note that all Roosevelt dimes minted in San Francisco between 1968 and 1978 lack mint marks.
This is because the San Francisco Mint was the only facility producing proof coinage during that time, and no mint mark was necessary to indicate the mint of origin for proof coins struck at that facility.
So, it is entirely normal for the 1975-S Proof Set dime to lack a mint mark, as it was produced at the San Francisco Mint as part of the proof set.
The absence of a mint mark on the dime in this set does not affect its authenticity or value; it is a characteristic feature of proof coins minted at the San Francisco Mint during that period.
In addition to the absence of a mint mark on the dime in the 1975-S Proof Set, it's worth highlighting some key features and coins included in the set:
However, finding one in good condition can be challenging, as these coins were struck more than two centuries ago and were subject to heavy circulation and wear.