Ok, I hit lvl 50 the other day and I gained CELL cammo on my scar. I find that odd as I was 20 or so headshots off the assesment lvl 3, so I'm guessing thats not how you get it.

Anyone know what you need to do to get this cammo, and what the weapon assemants do when maxed out?

You get the CELL camo for Scar for hitting 50.

You'll get a CELL camo for the Hammer after rebooting (prestige).

I don't know much past that because I haven't had much communication with people who willingly lost all their stats for a dull emblem and 1 dog tag.