I doubt that this sign went on a truck. Wouldnt the trucks signs just have been a decal or something?
I'm thinking that Jim is right about the trucks having decals.
As for the value of your sign, you are standing in a strange place & time. There would undoubtably be people in town who would love to have it. The reality is though, its just a sign from a local trucking, that only recently closed down. Stay with me here, there is a Tiger sign from a Denver oil company, that was thought of in the same way.
I'd be suprised if somebody would give $100.00 for it today. Though maybe next year, a bunch of former employees might chip in, and pay $300.00 for it, just so they can give it to their dispatcher for his 70th birthday, Mr. Whatshisname. Myself, I'd like to have a sign from two of our local trucking companies who are no longer around, but I doubt that I would pay anything more that what I carry in my pocket. And thats not much.
If the money is a concern, and there really is nothing wrong with that, an auction is the only way that you'll get any real money for it. If its for sentimental reasons, then the price is something that you and your buyer are comfortable with. In my experience though, any time I sell something, I wish that it never left here. I miss my stuff when it goes away...