The Washington Quarter was introduced in 1932 to mark the 200th birthday of President George Washington and replaced the previous Standing Liberty Quarter and became the second circulating coin to bear the image of an actual person.
Designed by John Flanagan, the Washington Quarter initially had a composition of 90% silver & 10% copper (referred to as Type 1) and beginning in 1965 the composition was changed to 75% copper and 25% nickel due to the rising cost of silver (referred to as Type 2).
The obverse features a portrait of Washington facing left with the inscription LIBERTY on the outer periphery above the portrait. Just below the chin of Washington is the motto "IN GOD WE TRUST". Beginning in 1968 a mint mark for Denver (D) and San Francisco (S) for proof issues was added to the obverse design just to the right of of Washington's ribbon at the base of the portrait. Beginning in 1980 a mint mark for Philadelphia (P) issues was added, prior to this Philadelphia issues carried no mint marks.
The reverse design features a spread-winged heraldic eagle, encircled by "UNITED STATES OF AMERICA" on the outer periphery above the portrait, and "E PLURIBUS UNUM" directly above, the eagle. The denomination "QUARTER DOLLAR" is below the eagle on the outer periphery and a wreath is directly below the eagle tail feathers. For coins issued from 1932 to 1964 a mint mark for Denver (D) or San Francisco (S) can be found just below the wreath. Philadelphia issues carried no mint marks.
No Mint Marks?
From 1965 to 1967, the mint issued quarters with no mint marks so there was no way to determine which mint issued a coin. At that point in time, there was a coin shortage and the mint director believed the shortage was created from coin collectors. To curtail what she believed to be the issue, mint marks were eliminated to deter collectors from hoarding coins.
The mint director's fear of collectors even went as far to eliminate Uncirculated and Proof sets for these years but would later issue a special mint set to satisfy complaints.
This mint director couldn't have been farther from the truth. The reality was that with rising silver prices and a planned composition change from silver to copper/nickel it was apparent to the general public that older silver coins were worth more from a melt perspective than the new copper/clad so the general public began hoarding silver issues more for melt value and less for collecting value. As circulating copper/nickel coins drastically increased, the mint would eventually understand this and returned mint marks beginning in 1968.
General Market Notes
Copper/clad or Type 2 issues can easily be found in pocket change while Type 1 silver quarters are routinely found in coin shops for only a small amount in uncirculated condition for common high mintage years.
For sleeper coins take a look at the 1937-S issue with a mintage of only 1,652,000 and for a more affordable sleeper look at the 1958 issue. With a mintage of only 6,360,000 the 1958 mintage is small for a coin issued after 1950.
Excluding error and proof coins, the key to the series are the 1932-D and 1932-S issues, while the semi-keys are the 1934-D, 1935-D and 1936-D issues.