What this coin looks like (obverse, reverse, mint mark location, special features, etc.): The 1938 D/S Buffalo Nickel is an RPM variety. The Denver mint stamped a D mint mark on top of an S mintmark hence the D Over S error. This is best indentified by a small portion of the S seen within the D and a small portion protruding out of the upper-right side of the D as depicted by the arrows in the example image of this coin above.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD