Thinking about Dave Winer led me back to this post about the London COVID memorial wall.  Turns out this was a grass-roots action.  I was back in London over Christmas, picked up a book by a group called Led By Donkeys (!) and turned to a random page, and the chapter was describing the process they went through to make that wall.  They spent a bunch of time figuring out what and where (opposite Parliament, so they couldn't ignore it), and then how to do it stealthily in such a way that it wouldn't be shut down by the authorities over the weeks that it'd take to complete.

They donned official looking hi-viz vests and made signs in official-looking fonts saying things like "National COVID Memorial Wall" that they glued on the wall prior to starting, and men-at-work hoardings that they put all over that section of the walkway.  The cops didn't pay them any mind until they were already well into it, and the media had started to cover it.  Eventually, leading from behind, politicians used it as a backdrop for press conferences.