Strictly speaking, you should sign the card as soon as you receive it, because the signature column is made of special materials, and it is impossible to sign it after a period of use! But in reality, almost all banks do not require users' counters to sign on it in order to save trouble or fear that their signatures will be broken. Generally speaking, it doesn't matter if you don't sign or sign other words. But in extremely special circumstances, once a legal dispute is involved, a card with a normal signature is the best evidence.