The CCV (Credit Card Validation) number is a 3 digit code printed on the BACK of your card in the signature panel. If there are more than 3 digits, the CCV is always the LAST 3, as shown below. This number provides an additional check on the validity of the card.

Card images

For Visa, MasterCard, and Discover this number is the last 3 digits printer on the reverse of the card:
For American Express the number is a four digit number of the front of the card: