Two choices. It's either a combination of a die chip inside the the D with some damage on the outside of the D due to circulation wear. OR...it's a repunched mintmark of some kind. From the images, I can't tell. This is the type of coin that has to be looked at closely and manipulated so that you can analyze the things seen at different angles in three dimensions. A flat image makes it tough to be sure and that's just the nature of a two dimensional image.
