Find the big black marker in Brutus room. It's located on the desk.
When that is done, you can see step 2 on Deadpools computer.
Now it's time to the in-game challenge. You have probably seen posters for recruiting to either GHOST or SHADOW. You will now "Deface" these posters. DO NOT DESTROY THEM. You just walk up to a poster, and then you will see an option to "Deface" the poster.
Once you have completed the challenge, by defacing 3 posters around the map, you will unlock the new "MERC" wrap.