The IWHBYD Skull is definitely one of the best challenges in H2 and its cool how it ties into H1. I always speculated that it tied into the rest of the saying so: "
I would have been your daddy, but the dog beat me over the fence". To me that seems to hint at a covenant or forerunner connection to the humanity where the "dog" is the possibly the Flood. But then I haven't played any of the newer Halos so I'm probably missing some newer clues or story info related to that by now.
We incorporated a few of the skulls into our custom campaign maps. The other day I was play-testing the maps; so I activated the built-in Camo button script and hit it again to increase the difficulty (which activates a few skulls at once), when you turn skulls on they tend to stay on (unless you are memory editing), so on the next map, a custom Coag, I activated the skulls again just to see what would happen and it said IWHBYD. LOL, my own IWHBYD on Coag. Personal achievements will always outweigh built-in ones.
So why the interest in the script?
You might be interested in this Cheat Engine 5.6 file as well:
http://h2mt.h2pc.org/tools/2_Vista/Cheat_Engine/5.6/
I forget which .CT file it is exactly, but I think its one of the .CT's labeled with Server or Engine, anyways it allows you to activate which skull(s) you want during SP.