type of credit card it is by the number. However long the series, ml, where is the 4 digit security pawn code on American Express. But do you really pay attention. They can be an additional measures of card security when you make online transaction. To know where to look for your card security code can be a bit of a hassle. Where to find the security code. Especially for those who havent made any transaction on the internet using the card. Discover card first digit starts with 6 and has 16 to 19 length. Though times are changing, the numbers on your card signify certain things that relate to your account. Visa card first number start with 4 and has. Just above your credit card number. The third and fourth digits have different meaning than the first two number. The American Express cards out there have not. American Express Card Security Code, either to the left or right of the embossed 15digit card number. MasterCard starts with 5 followed by other 15 numbers. The cardholder can find the security code on the front side of the card.