The War Zone plaque is a plaque contained in the Rikti War Zone co-op zone. It is not currently associated with any known history badge.
You are entering a "war zone". Check your fear at the door.
This plaque can be found at the door leading out of the red-painted wall of the Thin Red Line, a bit to the left as you exit through it.
Its coordinates are (1138.9, 0.0, -2091.2).