Randy, My sign and Cameo's are the gray bell version. They're are the harder version to find.
Can you please post pics of grey versions?
As to the original post, I've asked this quesiton myself some time back. Outside of maybe late 20's to early 30's, I dont think anyone has nailed it down any closer than that. If anyone does think they know, please let us in on it. Also only black and white picture from the era dont make it any easier to figure out. And from what I know, few if any Pennzoil signs from the era are dated.
