Card Security Code Validation The card security code (CSC) is a 3- or 4-digit number (not part of the credit card number) that appears on credit card. The customer enters the CSC on the Order Information form. Because the CSC appears only on the card and not on receipts or statements, the CSC provides some assurance that the physical card is in the possession of the buyer. About CSC The CSC appears on the back of most cards (usually in the signature field). All or part of the card number appears before the CSC (123 in the example). Example: 1. Visa Credit Card Users This 3-digit code is your Card Security Code (CSC). 2. Mastercard Credit Card Users This 3-digit code is your Card Security Code (CSC). For American Express, the 4-digit number (1122 in the example) is printed on the front of the card, above and to the right of the embossed account number. A. American Express Credit Card Users   This 4-digit code is your Card Security Code.