Visa, MasterCard & Discover Cards
The CID (card identification) number is the three-digit value printed on the signature panel on the back of Visa, MasterCard, & Discover Cards immediately following the credit card account number.
American Express Cards:
The CID (card identification) number is the four-digit, non-embossed number printed above your account number on the face of your card. This number is recorded as an additional security precaution.