Card ID Explanation Card ID - Visa & MasterCard The Card ID is a 3-digit security code that is printed on the back of your Visa or MasterCard. The number appears on the signature strip after the last four digits of your account number. The signature strip may contain your entire account number or just the last four digits of your account number. Either way, the Card ID will appear after the last four digits of your account number. The Card ID is used to verify that you have possession of the credit card you are attempting to use. If no Card ID is shown or you cannot read it Please tick the box There is no Card ID Number on my card