User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-181.165.4.114-20130806190106/@comment-50.152.54.131-20130806221759

So, yeah.

2nd letter: Takeo ("Emperor" hint)

3rd letter: Nikolai ("Motherland" hint)

4th letter: Dempsey ("Scuttlebutt" hint)