what you have is a common everyday worn and abused coins nothing special just reminds me of some quarters I get back in change
According to the Cherry Pickers guide (CPG), there are no varieties worth mentioning for the 1977 D Washington quarter. So no added value (NAV). Worth is 25 cents. Spender.
Welcome to Coin Talk. Your coin is not a doubled die. I agree that it's probably Mechanical Doubling (MD). Perhaps you could post a clear closeup of the motto IN GOD WE TRUST. Thickening of the letters usually occur when the die becomes worn. Also, filled mint marks like the D on the coin are very common and do not add any value to a coin.
Years of circulation mushiness and probably started off as a Deterioration strike. Not a Doubled Die. Also.. Mint marks for that year cannot be Doubled Die because they were hand punched onto the Die.
@Kiekie Mechanical doubling and Die Deterioration Doubling is relatively common adds no value. Error expert John Wexler has a site that lists known doubled dies and has a good explanation under the tab called "Worthless Doubling" http://doubleddie.com/144801.html It isn't easy finding true doubled dies