Visa, MasterCard and Discover Your card verification number is the last 3 or 4 digits printed on the signature panel on the back of the credit card following the card account number. This number is used as a additional security precaution.
American Express Your card verification number is the 4-digit number printed on the front of the credit card directly to the top right of the card account number. This number is used as a additional security precaution.