Card Security Code (CSC)
The Card Security Code (CSC) is usually a 3 - or 4 - digit number, which is not
part of the credit card number. The CSC is typically printed on the back of a
credit card (usually in the signature field).
On some cards, all or part of the card number appears before the CSC, for
example, 1234 567. In this example, 1234 are the last four digits of the credit
card number, and 567 is the CSC.
American Express Cards ALWAYS have a 4-digit,unembossed (flat) number printed ABOVE the account number like in the example below.