50's Pepsi Porcelain Sign...

[CocaMan]

Looks great cleaned up Jim!  I don't know if you have ever tried but there is a product called The Works toilet bowl cleaner that will take a lot of stain, especially rust, out of porcelain signs and you could try some steel wool grade 0000.  I have always had great results using both.  Make sure you wear gloves when you use The Works or you might feel a little burn on your skin.