Great. That way they can just sign it themselves. That way if a merchant does signature verification, it matches! And then when your CC company comes back and says "Chargeback is in dispute. The signature matches" you'll have to explain why you didn't follow the terms of the cardmember agreement.
Now, this is all very hypothetical for many reasons, but generally it's my practice to follow cardmember agreements that I am, after all, agreeing to follow.
How would the CC company know that the signature matched? At no point will the thief-signed card ever be sighted by anyone other than the merchant, briefly. The thief is going to dispose or destroy the card when they're finished with it; your bank/issuer is never going to see it to compare.
Now, this is all very hypothetical for many reasons, but generally it's my practice to follow cardmember agreements that I am, after all, agreeing to follow.