1. When using a ballpoint pen or gel pen, be sure to sign it at the new time. If it is used for a period of time before signing, there will be a layer of oil on the surface, which will be wiped off even after signing. The worst thing is to sign with a pencil.

2. If it is a debit card, the signature slip is basically useless. If it is a credit card, the merchant should verify the signature when spending. (There are still credit cards that require full name verification without password). Better sign it yourself.