Wikipedia doesn't think so, citing the US copyright office

https://commons.wikimedia.org/wiki/Commons:When_to_use_the_P...

There's a difference between reproducing a signature in an encyclopedia or in some way that makes it clear that you are recording the thing as it is.

Putting a signature on a work is forgery and in most jurisdictions charged as fraud.

If you produce an artwork in the style of someone and then clone the signature of someone who produces art in that style, there is a reasonable case for fraud.

No but in the article he makes the explicit case that its the mark of his trade.

CopyRight isn't the relevant legal concept here at all. It's more of impersonation through a specifically protected identification mechanism.