Visa
Visa's Card Verification Value 2 (CVV2) is a three-digit code that helps mail order/telephone order (MO/TO) and e-commerce merchants validate that the customer has a Visa card in his/her possession, and that the card account is legitimate. The CVV2 is located in the signature panel on the back of the card following your 16-digit card number.

Mastercard
Mastercard's Card Verification Code (CVC) is a three-digit code that helps mail order/telephone order (MO/TO) and e-commerce merchants validate that the customer has a Visa card in his/her possession, and that the card account is legitimate. The CVC is located in the signature panel on the back of the card following the last four digits of your 16-digit card number.

Discover
On the back of your Discover Card, there is an area where you sign your name. If your card was printed before July 2003, you will see two sets of numbers including your 16-digit Account number (see Card A) OR the last four digits of your Account number (see Card B). If your Card was printed after July 2003, you will see three sets of numbers (see Card C). These numbers are part of the state-of-the-art technology that we employ to enhance security and Cardmember convenience. The Cardmember ID number is used to verify transactions made when the card is not present, such as internet or catalog purchases.

American Express
American Express Cards ALWAYS have a 4-digit, unembossed (flat) number printed ABOVE the account number. This number is called the Card Identification Number or CID or 4DBC. Occasionally other 4-digit, embossed (raised) numbers appear below the account number; however, the CID is ALWAYS ABOVE the account number.