Visa, MasterCard, and Discover Requirements
Card Identification #REQUIRED
3 digit, non-embossed number printed on the signature panel on the back of the card immediately following the Visa card account number.
This number is recorded as an additional security precaution.

American Express Requirements
Card Identification #REQUIRED
4 digit, non-embossed number printed above your account number on the face of your card.
This number is recorded as an additional security precaution