Generally speaking, credit cards other than my own are not accepted internationally. As long as the signature is different from the signature on the back of the credit card, it cannot be used. If there is no signature on the back of the card, the customer will be asked to sign it before use, which is also clearly stipulated in the credit card usage rules.
It may be that the concept of using credit cards in China is insufficient, so some relatives will take their own cards to spend. In fact, if they don't sign their names, they can refuse to accept them. Merchants can't ask the bank for money without carefully checking the signature, and the losses are borne by the merchants themselves.