Something I stress a lot when doing walk-arounds at my workplace is that a union, while it has all this formal structure and dues and whatnot, is ultimately you and your coworkers coming together to fight and push for things that make the work environment better. Whether that’s preventing outsourcing, a higher minimum wage across the board, or pay raises for particular job classes, it’s not some scary outside force fighting on your behalf, it’s just you and your coworkers working together.

I’m in a pretty conservative city in a very conservative state, so you might have more luck with the more overtly “combative” language, but I’ve found making it very concrete and directed at the things you know your coworkers care about (i.e. what they think sucks about working there) is better received than anything with lofty political slogans or anything abstract. Politicization is incredibly important, but it’s hard to get people activated politically when they don’t even recognize/understand the power that they already possess. Smaller, but more attainable, wins demonstrate this power to people, and that can make it easier to politicize them further.
So I guess I’d emphasize more that you all are the union, and the union does what you all want it to. Whatever you do, best of luck, this is so cool to see! I’ve done a few years of union work now, so if you have any questions you can shoot me a message and I’ll try to reply as best I can!