DB shot me an email to see if I could add to this. I agree with Dick, it might be from a Alimite, but it also could be from a Grayco, Lincoln, or even Gilbarco. I did go through a 4" thick Alimite catalog and didn't see anything that looked like this. I did find this, where they state they can supply "Metal disc in actual colors. Diams. 4", 20". For reels, pump cabinets, oil bars, etc. Decals also avasilable." This was from around 1949.
Author, Gas Pump Identification book and Air Meter Identifiation book.
Over 500 auto/gas pump/air meter/service station images are now on my website, take a look: www.petrolianacollectibles.com