Conclusion: The three digits after the signature field of the bank card are actually the security code of the credit card, also known as the CVV code.

Credit card security codes are crucial for credit card holders. This is a set of 3 or 4 digits, which is generated by the bank extracting information from the card number, expiration date and specific service code, and processing it through a complex algorithm. This key is known only to the card-issuing bank and the cardholder himself, ensuring the security of the transaction.

Specifically, the security code generation process includes encryption algorithms, such as CVKA technology, and each bank has its own unique encryption rules. It is like an ID card for a credit card. It is not only used to verify transactions when shopping on overseas websites. It does not require entering a password. It only requires an account number and security code. Some domestic merchants also support the direct use of security codes when transferring money over the phone without a password. Therefore, keeping credit cards and security codes properly is the key to ensuring personal financial security. Avoid leaving credit cards out of sight in public places to prevent information leakage.

Understand and protect your credit card security code to ensure the privacy and security of every transaction. For more detailed information about credit card security codes, you can refer to authoritative information from Baidu Encyclopedia.