Card v е authentication number, card confirmation code/security code. This is a bank card used for indirect transactions such as online payment. Can identify whether there is a bank card transaction. It can generally be seen in the last three digits of a series of signature columns on the back of bank cards. The UnionPay standard card organized by UnionPay is called CVN2, MasterCard is called CVC2, VISA is called CVV2, and AE American Express is called CSC2.