One of those so-called "Mexican" threadless fence post topper insulator thingies. In a nice dark sapphire (?) blue. The actual origin and purpose of these glass curiosities is open to much conjecture, so here is mine:

Allegedly designed and hand-crafted by none other than world-class adventurer and bon vivant, [id=274721590; Manuelito Rasmussen Hemingray], who was then 110 years old, at his secret government "skunk works" laboratory near Scorpion's Forge, Arizona, in early July 1947, about the same time that the legendary Roswell UFO crash allegedly occurred. Perhaps ET from Zeta Ridiculi was in pursuit of this stunningly advanced glass technoloty ?