Not unless you actually tried to sell it for money.

If you just draw a cartoon with a fake signature, nobody is coming after you. Even if you posted on Twitter or something, nobody is coming after you.

You'd have to be fraudulently selling it in a book of cartoons or on coffee mugs or something.

>Even if you posted on Twitter or something, nobody is coming after you.

Are you sure about that one? Are you saying if you posted say, a racist cartoon on twitter, and you forge my signature onto the thing, I can't come after you?

I don't know about the US but here in Germany the category for this is personality rights. The entire point of a signature is to establish authenticity, using someone's likeness or identity without consent will get you into deep trouble even without money being exchanged.