Visa/Mastercard Users: Flip your card over and look at the signature box. You should see either the entire 16-digit credit card number or just the last four digits followed by a special 3-digit code from the right hand side. This 3-digit code is your Card Security Code.
American Express Users: The American Express Card Identification Number (CIN) is a four-digit number found on the front of the U.S. issued American Express Card (including Optima). The security code is located just above and to the right of the credit card number. For the Optima card, it is displayed on the front of the card, to the left and just above the credit card number. American Express and JewelryVortex.com are now using this number for added security and customer protection.