What this coin looks like (obverse, reverse, mint mark location, special features, etc.): One major variety is the 1950 S/D Washington Quarter. This variety features an San Francisco "S" mintmark struck and punched over a Denver "D" mint mark (OMM variety). It is very easy to spot this prominent variety. The best way to identify this coin is to note that the openings within the "S" on the upper-right side and lower-left side of the "S" are closed up by the "D". Parts of the underlying "D" mintmark are seen within the "S" and slightly outside of the "S" as well. These features are depicted above in the example image.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD