@CW, first welcome to CCF. Second, your pics are good, but rotated by 90 degrees. I think that this may happen when you take pics with your camera held vertically rather than horizontally. In any case, I think that I see what you are talking about. I'm quite sure that these are actually small areas of damage that are vaguely D-shaped. For your reference, here is a link to the known '52-D RPMs. Typically these mintmarks are overlapping rather than completely separated.