I agree, part of the die. Very strange. Reverse looks like a very early die state. Maybe, just spit balling, but perhaps this is normal for the first...I don't know....10 coins from each die. And they quickly get polished away by metal flow since they are raised? Honestly just throwing out the first thing that comes to my mind. As an Engineer...it kinda makes sense.
What it really is...( shrugs).