The Card Verification Code is a three or four-digit number located on your physical credit card that provides an extra layer of security for credit and debit cardholders. The location of the CVC depends on the card type. For Discover, MasterCard, and Visa cards, the CVC is the last three digits of the number that appears on the back of your card in the signature bar. For American Express, the CVC is the four digits located on the front of the card, on the right side.