If you want to stop the sign stealing .. set up a watch patrol in your neighborhood, or buy a little video CAM and set it up on your front porch and record who comes into the yard and takes the signs.
Take a copy of the video to the police. Call the media and complain. If you have a good ally in the media you can trust, give them a copy of the video. The public might recognize the persons doing the act.
Just a thought!
That's a good suggestion except we only own a camera. Maybe it is time to go for a camcorder and hide out on our porch.