I think he means something like fingerprinting or image file version identifiers.
Let's try the easiest one put a what string at the beginning of a string. Put this near the top of your code
static char *MYidentifier="@(#) programname version 1.1.0";
ident and what will display it for you. You can write your own ident module -
call strstr() to find the start of the identifier.