Flip your card over, and look at the signature box.
You should see either the entire 16-digit credit card number or just the last four digits followed by a special 3-digit code.
This 3-digit code is your Card Security Code.
American Express Credit Card Users
Look for the 4-digit code printed on the front of your card just above and to the right of your main credit card number.
This 4-digit code is your Card Security Code.