Ask Lemmygrad

Honestly, depends who the artist is and how you're using the work. Prime example is the Neo-Nazi Stonetoss, all the parodies and reworkings of his memes have the name removed or parodied to mock him.

If you're just taking a random persons artwork, then its probably best to leave the signature and credit them.

I think it's fine to leave the name as long as the edit makes it clear that the image has been edited.

Alternatively, add "Original by" above / in front of the signature.

I think editing the original artist's signature just like you edit the piece itself, could be a cool touch. That way you indirectly 'refer' to the original artist but also make it clear that you're not them. You can kinda play that artist's communist alter ego that way.

Mentioned that it has been altered by you if you do leave it in. Creating openly communist artwork can destroy artist's careers in quite a few parts of the world, it wouldn't be fair to them if people see the edits and assume they are a communist if they aren't (or they are, but they don't want their professional work tied up with their personal work)