First, the bank may require signature on blank paper to ensure the authenticity and traceability of the signature. The bank will record your signature on blank paper and compare it with the signature in the identification documents provided by you to ensure the authenticity of the change application and your true wishes. This can help banks ensure the security and legality of transactions.

Secondly, the signature on blank paper can be used as legal evidence. If there is a dispute or dispute after the change of your legal representative, the bank can use your signature on blank paper as evidence to prove that you have agreed to change, and it can be used as the basis for relevant legal procedures.

Finally, the signature on blank paper can prevent tampering or modification. Because there is no other words or content on the blank paper, only your signature, which can reduce the possibility of others tampering or modifying the signature. This can improve the security and reliability of the transaction.

It should be noted that the specific rules and procedures of banks may vary from region to region and banks. If you have any questions or concerns about the bank's requirement to sign on blank paper, I suggest you consult the bank staff for more accurate explanation and guidance.