The die crack is a sign to help identify the stage of the coin which is stage three. Pcgs has two coins graded at ms64, au58 both have the same exact details
If it's a rpm. On the variety list for possible rpm this has all details of the type of die that this Carries as a rpm. Stage c with a hairline crack on the head going to the letter on the obverse and reverse has a rpm no sign of machine doubling on either or of the faces of the coin but pcgs has two quarters that are graded with ms64 and au58 that have the same exact detail as this quarter. I strongly believe this is a rpm. I almost kicked out of a group on Facebook for saying its a rpm and proved examples of a rpm for 1964-d Washington quarter..
The D looks to match the images shown on CoinFacts for the FS-501. I can't tell much from the images in the CPG. Neither say anything about a crack on the head. At this point, I'm not sure what you have.
My thoughts. 1. I don't think it's 501. It's a very lightly punched RPM ,much further to the East. 2. It is possible for only the mint mark to show MD. 3. A lot of Washingtons have die cracks in that area. It alone can't say you have an RPM. It can be used to ID a particular RPM, but it has to be in the same exact area as the RPM in question. Here's more RPM's from Wexlers to explore. http://www.doubleddie.com/1237766.html
I'm goi with a fs501. Pretty evident that t is a rpm even like I said pcsg has graded them but it's easier on my part to sell unplanned the. Slabbed. Will only get a ms60 max but I see a au58. Also the die crack is a guide to assist you to find a rpm and this is surely a rpm. But I am happy to all opinions of how others think! I don't wanna argue with people saying no or yes .. We share we all share ideas till the truth gets nailed to the board!