In FFIX each card says something like "0P00".
The first character is the card's attacking power in hexadecimal. Well actually, a 0 means the card has attack power "0F" in hexadecimal which translates to 15 in decimal, a 1 means the card has attack power "1F" in hexadecimal which translates to 31 in decimal, and so on, up to F (F is 15).
The second character is the card's attack type, P (physical), M (magical), X or A. I'm not sure what X or A means, someone else will have to explain that
The third character is the card's physical defense, denoted in the same way as attack power.
The forth character is the card's magical defense, denoted in the same way as attack power.