Lincoln cent 1964 D DUAL MINT MARK

I found and interesting object, or "D" on the neck. I noticed it in plain site right next to the beard.  So i said  "hey that looks like a letter." Used my 20x loop, and yes it looks like a D. I put it under my USB electronic microscope that magnifies 37x and its clear to see that there is a d.    I compared 4 other 1964-d lincolns of similar grade. Some were a tad better and some a tad worse. I would suppose that from wear and tear over the years the coins smooth out and the detail should be lost. This detail, or possible dual mint mark on lincolns neck sticks out. To me it seems like another mint mark. I am not sure if there are variaties similar to the neck mint mark. i have seen numerous pictures of dual mint marks but none this far apart.  I have found only one other RPM in my pocket change. I believe its a letter, I believe a D mint mark. Maybe its another part of the die like God or the B in liberty. please take a look at the picture.  Id like to get it verified by those online before i send it to a professional service. I think this is a very intersting find. thanks