On the back of most credit cards, all or part of your account number is displayed in italic font across the signature strip, followed by 3 extra digits (as shown below). For American Express, a 4 digit number is printed on the front of the card. This is your Card Verification Value, or CVV.

CVV is an anti-fraud measure being introduced by credit card companies worldwide. It is required that you enter the CVV printed on your card each time a payment is made and you are not present to sign a receipt, as for on-line transactions.