For the first question, you can't prove whether he checked it, but you can get the signature form (all major card organizations provide this paid service) and then do handwriting identification to prove that you didn't sign it. The second question, of course, is not stealing brushes. That is your own responsibility. Who told you not to sign it? Moreover, all credit cards in China have passwords, and you should bear at least half of the responsibility for being stolen, because you have not kept your passwords well and have not been stolen abroad. According to the current jurisprudence, you need to bear at least 20% responsibility.