CVV is an anti-fraud security feature to help verify that you are in possession of your credit card. For Visa/Mastercard, the three-digit CVV number is printed on the signature panel on the back of the card immediately after the card's account number For American Express, the four-digit CVV number is printed on the front of the card above the card accountnumber.

Visa/Mastercard American Express
Visa Card CVV Image
A 3-digit number in reverse italics
on the back of your credit card
American Express CVV Image
A 4-digit number on the front, just
above your credit card number