https://cohost.org/roguecache just made a new solarpunk logo; i think it's very well designed and keeps the simplicity while still keeping sun, nature and technology meanings
This would lend itself to stencils pretty well though (one color, no islands), especially with a touch of spray adhesive on the back. I've done the symbol from one of the more common solarpunk flags, and getting the blank spot inside the gear positioned would be a little finicky if doing graffiti.
You'd want to bridge the corners there, to make it all one piece, if you wanted to be able to put it up quickly. I was just painting a laptop so I had plenty of time to fuss with it.