In the middle curve on the left, it is not a smooth turn of the" S" and the right side looks almost straight instead of curved.
Although I'm not a Die Variety specialist, I think you're looking too hard for something 'different'. That "S" Proof mintmark looks fine to me, but I'll be glad to hear what others say. It might look like there's 'something' there, but I believe that the die just struck a lot of proofs, and this is what the MM looks like after awhile. I don't see any evidence of it being repunched. What do the others say ?
