Black sharpie, it's signed on the thick clear plastic you would use to protect an album cover. Per seller, was signed outside an AC/DC concert he attended.
Authenticity check is pending (live, not quick opinion).
It has some positives, and also some negatives. My biggest question is why would you want a McCartney signature that is this badly smudged, especially on a clear plastic toploader? There are plenty of nicer signatures on better items that are affordable.
I agree with Devon's question and point. If genuine, what would you do with it? If genuine, it should be severely discounted IMO as it is so...fragile. A butterfly wing might be more permanent.