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.
Per the terms of the cardmember agreement that you agreed to, you are required to sign the back of the card. If you do not, you are not authorized to use the card for any transactions.
It's all very silly anyway given that online credit card transactions almost never require a signature.
Quite honestly though, once a thief has access to your card, you have other problems. If they're close enough to see it, they're likely close enough to duplicate it and leave you the card with you ever knowing.
If the signature is that concerning, then use one signature consistently for your credit card transactions that's unlike the one you use for anything else.
If you don't like that option, then you probably shouldn't be using credit cards currently offered.
