I would guess it came off a larger esrly outdoor sign? Much like the small bowties that go on bottom of the OK Used Cars keyhole shaped porcelain neon signs? Have you ever seen a sign bolted to a lubester or pump with a flange like that? I have not. The lettering and way the sign appears almost looks like some of the European signs you see? I have nothing definitive, just my opinion based on what I've seen collecting Chevy items for last 20 some years
. Gmstuff should be able to offer some insight, he is very versed on Chevrolet.