Put signs up where you can keep video of them. Record video of them being stolen or vandalized. Share the video. Video of the other side acting badly is even more valuable than the signs.
Put the signs inside a plexi case and anchor that into ground very well. Stinging/burning gel on back. Vaseline impregnated with broken light bulb fine fragments smeared on it.
“Video of the other side acting badly is even more valuable than the signs.”
People have been seeing “the other side acting badly”, e.g., murdering people, burning cities, destroying entire stores. I doubt if posting video of a sign being stolen will catch anybody’s attention.
I think inflicting immense pain in some way is the only way to go.