Yes, it's a pair of glasses. The Thing is a magazine that comes to subscribers as a different object every time. This is what they say about Lethem's issue:
Jonathan's issue is entitled the "Chaldron Optical System." It relates to his upcoming novel CHRONIC CITY and consists of a glasses case, a pair of clear glasses with text on each of the arms, and a care and maintenance manual written in both English and French.
I'd like to see the Kindle version of this.