Sorry, while I marked it bug, I expected to be told that it was somebody's logo. I didn't know there was an in-game reporting tool, but I just found it and submitted it there.
I'm on Ultra graphics, with a 4k screen. I was standing on a radar tower on the highest mesa to the west of the easy starting area near the left edge of the map, with the radar tower near coordinates X=-150151.84, Y=293028.72, Z=18869.36, R=154.50
By the way, when I went back, the shape was different from the image above, so I guess since it's changing it must be bug related and not a logo.