I did attend the rally In Olympia. Having never been to one of these before, I was a bit unsure what to expect. What I found was a crowd of absolutely normal people. Granted very nearly all of them were packing weaponry, ranging from one guy with a sword to the latest in the AR platform and everything in between. My choice to carry at this event was an M1 carbine. There was much handing back forth of these weapons as well as some selling and buying, all in plain sight. Other than the defiance against our new law, there were no incidents of any kind, not to mention, the only thing even close to being trashed was the lawn the event took place on.
There was a very noticeable presence of the Washington State Patrol and all of them were obviously relaxed and not too worried about misbehavior by the protesters. There were also folks from other states here, most noticeably from Oregon. Even the LGBT folks showed up and had a table with some guns on it and they were inviting people to handle them (not legal for the new laws definition of "transfer").
I did not get to stay for the whole rally as I do work for a living. But when I left there were over a thousand people a the rally. WSP did estimate as many as 2500 eventually showed up though the numbers were downplayed and reported to be much less by the local media.
The fun on this one is that they (the folks in power) admit they have no idea how to implement this, basically halting any "transfers" that aren't first time sales from an FFL
Videos of the speakers at the rally
The Prosecutor and Sheriff in my county aren't even going to bother with this law