What is a credit card Security Code and why is it required? In order to protect you from unauthorized transactions, we require your credit card's Security Code MasterCard, VISA, and Discover: The Security Code is the 3-digit number printed on the signature panel on the back of your card. It immediately follows the account number. American Express: The card Security Code (also referred to as the CID number) is printed above the imprinted card number on the front of the card (on either the left or right). ** ** Please note, there are a small percentage of "plastic-less" card accounts for American Express - Corporate and Purchasing Card accounts. If you have one of these accounts with no AMEX card, please enter 5555 as your card security code.