1. Signature is irregular or inconsistent with reserved signature. Banks need to sign for confirmation when handling bank cards. If the signature is not standardized or inconsistent with the reserved signature, the bank staff may ask for a new signature or refuse to handle it.

2. The certificate information is inconsistent or the certificate has expired. Banks need to check the identity documents of cardholders when handling bank cards. If the certificate information does not match or the certificate has expired, the bank staff may request to update the certificate information or refuse to handle it.

3. Identity information is fraudulently used or at risk. Banks need to verify their identity information when handling bank cards. If the bank suspects that the cardholder's identity information has been fraudulently used or is at risk, the bank staff may ask for more identity documents or refuse to handle them.

4. Banking system failure or network problems. Bank system failure or network problems may lead to unsuccessful signature. It is recommended to try again later or contact bank customer service for consultation.