The ring piece had a special ceramic-like insulator clipped to it. The insulator held high voltage wire used on some neon signs. Your Packard sign is a small section of a larger neon sign. The thin angle piece is just a brace to strengthen the panel.
Yeah, I confirm what Yeley is saying. It's to hold insulators on the older '40s-ish neon signs. My Firestone sign had these too. They worked with brown insulators that clipped in like in this picture. You can see a few that I didn't use because I changed the routing slightly. This is back when they used copper wire to connect rather than GTO wire.
