Credit card numbers have a specific purpose. ... The first digit of the credit card number tells you if the card is from American Express (3), Visa (4), Mastercard (2 or 5), or Discover (6).

For Visa, Mastercard and Discover cards, you’ll find the three-digit code on the back, usually inside or just above the signature strip. American Express does things differently, placing a four ...

Your credit card's security code is a three- or four-digit number that helps protect you against credit card fraud. Learn how to find it and why it's important.

Each type of account number has specific lengths, which can serve as a secondary method to identify the type of credit card. For example, Visa account numbers can be up to 19 digits.

With most credit card networks, including Discover, Mastercard and Visa, you'll find the security code on the back of your card, to the right of the card number.

The security code for American Express cards, commonly referred to as the Card Identification Number (CID), is a four-digit number located on the front of the card. Unlike Visa, Mastercard, and ...