It's some sort of spot...in which the toning stopped but then began again in the middle like a bull's eye. I have a few 1894 proofs and one specifically with a few marks like that. It ends up being a black hole of a dark spot on an otherwise colorful piece. I'm ok with it just being the 1 marker on this on this piece. My other 1894s albeit graded do not look as nice as this. I also picked up an 1883 proof which I will up in a bit.