What this coin looks like (obverse, reverse, mint mark location, special features, etc.): One major variety of the 1875 S Trade Silver Dollar features the Type 1 (Type One or Type I) Reverse.
The Type 1 reverse was the earlier design used on Trade Dollars minted from 1873 through 1874 and some of them from 1875 through 1876. This design features an extra berry on a branch under the eagle claw on the right side of the portrait. In addition: The bottom-most arrowhead tip ends just above the "0" in the words/numbers "420 GRAINS".
The Type 2 Reverse is a newer design used on some Trade dollars in 1875-1876 and on all Trade dollars starting in 1877 and onwards. This design is missing the berry under the eagle claw and the bottom-most arrowhead tip ends just above the "2" in "420". These features are depicted below. The difference between the 1875 Type 1 Reverse vs Type 1 Reveres Trade Dollar is depicted below in the example comparison image:
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD