The George Washington quarter first came into circulation in 1932. It was designed by John Flanagan, whose initials appear at the base of Washington’s neck. They can be hard to spot, since they are one of the first things to wear off of the coin.
For silver coins before 1964, the mint mark appears just below the wreath on the reverse side. Coins with “D” are from Denver, with “S” are fron San Francisco, and those with no mark are from Philadelphia. The San Francisco mint only produced quarters through 1954, but reopened in 1965.
Starting with the switch to copper-nickel clad coins in 1965 and through 1967, the quarter shows no mint mark, even though coins were produced in Philadelphia, Denver, and San Francisco.
The standard method of using D for Denver and no mark for Philadelphia resumed in 1968, but with the mint mark appearing on the obverse side to the right of the nape of Washington’s neck. That year the San Francisco mint ceased producing quarters for general circulation and switched to striking limited-run proof coins for collectors.
In 1980 the letter P was added for Philadelphia. This continued through the state and national parks series of quarters.