Copied from another site, pretty interesting thought:
"Honestly while a non reveal, there is a bit more to it... while the obvious first tought is Spiderfang goblins (wich I would like very much), I think they are excluded because of the chaos comes scuttling from below...
Which could possibly mean Ashcrawlers
And if Ashcrawlers are their own distinct warband, its very possible the other symbols indicate a new wave of unique warcry warbands.. and while its odd to start this late after the book they featured in, keep in mind that its quite possible that whats coming for warcry now was supposed to come much earlier."