So I finally figured out what it was

[TinCanAlley]

I had noticed that the apartments in a building I do work for had an electrical outlet that didn't work. They had long been painted over and ignored. I figured they were old non-polarized plugs and left there when updated in the 50s to newer and more outlets in each place.

A while back I decided to free one from its tomb and it was a single outlet with two wires connected to it. I put a plate over the box and took it home. When I got home I started to clean it up and it turns out that it's not an outlet for power, but an outlet for radio antenna. Seems one side is ground and the other goes up into the attic of the building where there's a long copper wire run the length of the building.

I looked all over the internet for these things and can't find anything of use. I gave it to my brother as it seems his house also has the wire in the attic, but his outlet was removed years ago. He now has his old Philco hooked up the proper way.