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.