On a Visa or MasterCard please turn your card over and look in the signature strip. You will find (either the entire 16-digit string of your card number, OR just the last 4 digits), followed by a space, followed by a 3-digit number. That 3-digit number is your card security code. (See below)
On American Express Cards, the CID number is a 4-digit number that appears above the end of your card number. (See below)
This is a security measure we require for all transactions. Since the card security code is a number is listed on your credit card, but is not stored anywhere, the only way to know the correct number for your credit card is to physically have possession of the card itself. All VISA, MasterCard, Discover and American Express cards made in America in the past 5 years or so have a security code number.
This number is printed on your MasterCard, Discover, and Visa cards in the signature area of the back of the card. (it is the last 3 digits after the credit card number in the signature area of the card). IF YOU CANNOT READ YOUR CARD SECURITY CODE, YOU WILL HAVE TO CONTACT THE ISSUING CREDITOR.
American Express cards show the card security code (also referred to as the CID number) printed above the imprinted card number on the front of the card (on either the left or right).