It looks like something added post-mint, maybe a counter mark/sign/strike of some kind…and it could be a stain, it doesn’t appear to be raised, hard to tell from the pixelated close-ups. One thing is for sure: The Mint did not create a special die and use it to strike this type of coin. If they had, many more of these would have turned up by now. …imo…Spark
I do It doesn’t appear to be raised and is definitely part of the coin but I don’t think it is a stain. The straight edges and square shape makes it seem intentional to me.
i still trying to get better images than of the ones I’ve posted. The best image is the 1st one expanding the view of the coin. I don’t think it is a stain. The straight edges and shape definitely look intentional to me.
