I'm no attorney, but maybe a speed bump in the Mayor's plans?
RCW 9.41.300: Weapons prohibited in certain places ? Local laws and ordinances ? Exceptions ? Penalty.
(2) Cities, towns, counties, and other municipalities may enact laws and ordinances:
(b) Restricting the possession of firearms in any stadium or convention center, operated by a city, town, county, or other municipality, except that such restrictions shall not apply to:
(i) Any pistol in the possession of a person licensed under RCW 9.41.070 or exempt from the licensing requirement by RCW 9.41.060
I see that this is your first post on USA Carry, Glock 26. Congratulations.
Anyway, the information you've presented seems pretty cut and dry to me. Anyone with a CWP (or whatever they're called in Washington) is perfectly within their rights to carry on city owned property regardless of what kinds of signs he posts. Maybe a group of you CCW holders could do a protest march while carrying and have a copy of that law with you. Just a thought.