You're kidding and here I am reading you and thinking, OK, I can get a car battery, put some baby jumpers on the terminals, string the other jumpers, one to each of the outer posts holding the sign, while having the battery in a moisture proof casing and buried out of sight. And since those outer posts will be the first one's the vandal will touch and likely with a metal cutting apparatus they brought for the zip ties, POOF!
What a story they'd have to tell. I tried to steal a Republicans political sign and all I got was these third degree burns.