What is a Card Identification Number (CIN)?
Discover® credit and debit cards have a 3-digit code called the "CID" (card identification number). It is not embossed like the card number and is always the final group of numbers printed on the back signature panel of the card.
NOTE: This is the second code of the Card Security Code
Electronic Merchant Systems Payment Processing Glossary :
Defining key payment processing and merchant services industry terms to help business owners make better decisions.