I will admit that I have Rockwell Test Marks on the brain, but I am considering the possibility that this may have been from a test mark on the die. This feature, however, appears to have a tiny bump in the very center and it does not look really smooth, which it should be for such a mark to be considered seriously. While you may not be able to obtain a clear photo with greater magnification, it may be possible to look at it through a stronger loop and tell us what you see. It is about the right diameter to be one.