User blog comment:Argorrath/Treyarch posts a message of zombies; possibly hinting to a DLC 4/@comment-184.5.98.212-20130731223812/@comment-176.253.248.29-20130731230136

Exactly, the only thing i've gathered from the 4 letters is that it seems likely this prototype German armoured weaponry is perhaps going to play a role in the next map, especially as all 4 seem to be writing about visiting it and witnessing it. But who knows? Maybe it's about the characters though, there's just no clear idea yet.