I will be in the minority but all 6", 8" and 10" heavy porcelain sunray signs might be fantasy.
Several were made circa 1979 and again in 1989 at Sourhwestern Porcelain in Sand Springs OK. Earlier versions have a dark gray back and later ines a lighter/medium gray back. All have split grommets and excellent shelving.
I've never found any compelling evidence that these were used on pipelines or even pumps.
Even if there are a few originals the majority are older high quality reproductions made at a now defunct porcelain sign company.
Collect small Oklahoma Oil Co.'s 1920's-1940's. Barnsdall, Cushing, Eason, Marland, etc.