Is this a Repunched Mintmark? It would be my first. It looks like a tilted D over a Flat D. In the 3rd and 4th images it appears to have signs of the second D on the inside bottom of the first D. When you are looking straight at the coin, like the 1st picture, the back of the D's look like two clock hands when they are close together. You can see that with a magnifying glass. When looking from the southwest side, it looks like you can see a tilted top D on top of a flat wider backed D with portions of the flat D on the inside of the D like doubling. Mostly you can see the sepeartion of two D's in the Back of the D's when looking from the southwest.
Sill learning, but the flatness indicates mechanical doubling from what I understand. I think you are looking for split serrifs on the D. Looks like a little notch at the corner. Also looking for the second impression to be rounded. I could be wrong though, I was once before in 1984.
split serifs are a great indicator of a true doubled die, but are not always necessary, nor are they obvious. the shelflike look and the narrowing of the letter leads me to think it's mechanical doubling and maybe some die wear as well. Mintmarks are a high point in many coins or at least they are isolated from the rest of the design and they take a beating during the minting process so they are easily distorted.
