Just as before with the Double Fine paintjob, you can signup for the newsletter to get the Brutal Legend DLC items, a jacket, mullet and a flame paintjob. The cotent apparently gets pushed out sometime after Feb 29th, 2012, when the signups end.
It has also been alluded on the official forums
that the Double Fine Orange Camo paintjob is also going to be included.
Signup here: http://www.ironbrigadegame.com/enlist.html
*This is the official web site for the game run by Double Fine, developers of Iron Brigade (Trenched).
Limited time offer, expires Wednesday February 29th, 2012 at 11:59PM (timezone unknown, probably wherever DF is located).
ps. - If it's anything like what was done before you should be able to sign up your friends by simply putting in their Gamertag and putting in a fake name/email. That is what I did in summer '11 for a few friends for the Orange Camo and they ended up getting the DLC. I never received any newsletter(s) and used fake name/email for my friends when I signed them up.