Growing up, we had a few of these glass bell insulators that my dad collected tucked away in the garage. Originally, they were designed to keep the wires linking telegraphs and telephones insulated from the wooden poles. I occasionally still see them atop telephone poles, though I’m not sure if they are serving a purpose or if they’ve just been forgotten by time.
Though it’s not particularly unusual to come across them, I can’t remember ever seeing any attached to a building before. I spotted these attached to a four-plex near the University of Kentucky’s campus. Have you come across this?