I've seen videos where signs were wired, delivering a shock to the thwarted thieves.
Those fence chargers run $50 and come in 12VDC or 120VAC. They put out 2,000 volts in milliamps.. Most municipality or state laws require a danger sign be posted, which I guess you could attach to the political signage. They hurt. I used to buy the low impedence brush burners for $100 each. I fenced about 80 acres of pasture with them. A little one would take about an hour to rig up properly and about $20 in insulated HV wire on the ground to the sign frame and a good ground rod wire around the sign in the dirt.
You could get sued for shocking someone as a booby-trap. I remember the farmer who reinforced his mailbox as to thwart the baseball bats knocking them down by teenagers. A bunch of kids were blowing them up with M-80 firecrackers one night and because he reinforced his mailbox the blast came back out at the kids and the shrapnel cut one’s artery in his neck. He bled out in five minutes. The farmer was sued for millions and the jury found him at fault for modifying his mailbox to be dangerous. Cost him everything.