The first four digits of the signature column are the last four digits of the card number, and the last three digits are called "the last three digits", which is the password verification code for card-free transactions, that is, the verification code used by cardholders to verify their identity when making card-free consumption.

Take Bank of Communications credit card as an example. The last three digits are verification codes (also called "the last three digits"), which are the most useful and used for online transactions. The verification code of credit card is called CVV code. It is a series of 3-digit numbers generated by the card number, expiration date and service constraint code, and by the coding rules and encryption algorithm of the issuing bank.