802 South 8th Avenue: What's this?

From time to time I see a mailbox with parts I can't identify. Here's one:

I also can't figure out why it needs a curved post. (Hmmmm… I guess the post fits with the general weirdness of the box.)

If you have a clue, please leave a comment below. (You can be anonymous.)

I drove by — and scratched my head for a while — on March 16, 2022.