It could just be the ribbon on the Minute Man's ponytail has been polished away. I did an overlay of the coin to check if it might be a clash mark, but it doesn't match.
Here are a couple of images from PCGS. It looks like it was a problem area. Lots of images show the details in this area are missing.
Click on the photo for a lager image
ANA ID: 3203813 - CONECA ID: N-5637 Clean a coin that may be worth collecting? Please DON'T! When in doubt, leave it dirty!!
