I won the eBay auction for this odd glass object identified as an insulator, but it isn't. I think it is a sidewalk prism, aka vault light, aka pavement light. I am having the foremost expert in sidewalk prisms take a look at it, but he hasn't gotten back to me yet, so I am opening it up to the collective wisdom of ICON to see if I can get a solid ID on it. It looks like a squarish, ribbed inkwell with a squarish opening and is embossed on four sides: BERCER'S / SQUARE / BULL'S EYE / No 5 . It is 2 and 3/4" by 2 and 3/4" and 1 and 3/4" tall.

This is a glass sidewalk light/prism manufactured by the Berger Manufacturing Company of Canton, OH. The "BERCER'S" embossing is apparently an embossing error of "BERGER'S"