For the first question, it is impossible for you to prove whether he has verified it, but you can retrieve the signature sheet (all major card organizations provide this paid service), and then do handwriting identification, so as to The certificate is not signed by you. The second question is of course not considered plagiarism. That is your own responsibility. Who told you not to sign? Besides, domestic credit cards all have passwords. If you are debited, you will be responsible for at least half of it, because you did not keep your password well, and it was not stolen abroad. According to current jurisprudence, you need to bear at least 20 % responsibility.