I guess it depends on what type of sign...there were the type where the neon was the main component of the sign, like the old Dad's Root Beer plant, or others where it was just an element, like old hanging tavern beer signs where the only the outer border had neon tubing.

I read that neon was a big part of the Century Of Progress environment, for signs and general atmospheric lighting, and that neon signage had only really been around in the US about ten years prior.