Has this been verified even a little bit?
This poster has been around the Seattle area since around the time of the 2016 election. The Antifa group named in it claims to have had nothing to do with it - even going so far as blaming it on the "alt-right" and even on Milo Yiannopoulos... some sort of "smear" orchestrated against them.
So, the poster is real, it's been spread around in the AO of "Emerald City Antifa", but they blame it on their enemies. Note that the Antifa disavowals carefully avoid disagreeing with the *message*.