The whole lights and signs thing on this site cracks me up!
I'll tell you right now, for the first 2-3 years I was a spotter (back in the mid 80s), I did not have any signs. It was actually the Sheriff that asked our Civil Defense director to come up with signs for his spotters because the Sheriff was tired of being called out by land owners who wondered who the stranger was that was parked out on the road by their land. So, they printed up these hidious stickers that said "Tornado Spotter"! I hated putting that damn thing on my beloved Trans Am (yep, with the big chicken on the hood!), and didn't use it the 2nd year. I was sitting on a county road one night around 1am, spotting, and a pickup comes up behind me and stops. Next thing I know, a rancher is standing next to my car in the dark with his shotgun wanting to know what I am doing. Scared the living hell out of me. I paid for magnetic signs myself, and have used them ever since. There is a reason the electric company has signs on their trucks. They are not trying to be a "show off". They want the public to know what that white pickup is that is parked in the alley behind my house with a man sitting in it.
I think they are a good idea, especially in rural areas, but I'm not going to ride other people to get them. To each their own.