I was at http://www.mortalkombatguides.com/ and saw this:
For the PS2
Go to:
Game Options: Gameplay
then hold down
L1+L2+R1+R2+select+ Square
for 12 seconds
then at the bottom right corner of the screen
the number will appear.
For the Xbox
Go to:
Game Options: Gameplay
then hold down
L1+R1+White+Black+X+Select
for 12 seconds
then at the bottom right corner of the screen
the number will appear.
looks like it might be the ersion #