How to get signature images to work with non-numeric ID's?

[Infernette]

Okay, I have it set to where your creatures get a random code when you adopt them, but it's causing a problem with the signature images, which I cannot seem to fix.
I was wondering how to make it register the different, non numeric id's instead of just the numeric ones ( I can get it to register the numeric ones images to work just fine.)
I'm not exactly familiar with how the siggy part works and where it is, just a pointer as to where it processes that and stuff would probably be good enough for me since I know how to set it to work with non numeric things I just lack the knowledge of the location of the siggy image part