Idle hands are the devil's workshop, my grandmother used to say. But sometimes the devil's workshop is manned by idle geeks who have a message to send to the world and have found the perfect medium: the road sign.
Give a geek a forum and he'll prove just how geeky he really is. I mean, sure, there are people who hack road signs and just broadcast infantile displays ("I made the sign curse!"). But geeks will kick it up and warn people about alien invasions, flying monkey infestations and all manner of impending zombie attacks.
And, hey, one of these days, one of these signs could be right. (Please be flying monkeys.)