you've seen it all before, I know...

I love people watching.  And I have found that there is nowhere better to do this than a NYC subway.  I have seen everything from a lady applying roll-on deodorant (why can't this wait until a bathroom?) to a man forgetting he had a cello strapped to his back (this ended poorly).  But nothing has baffled me more than this.  On multiple trains (C,E, N/R/W), in random cars both old and new, I have looked up and seen this sticker.  

I have no idea what it is, if it is part of the train, or if there is some random dude sticking thermometer stickers on the ceiling of cars.  I have made checking for these stickers part of my subway routine - and am always baffled by their lack of/presence.  I am always weirded out by people taking pictures on the train, but decided to get over it and took these on two different morning commutes.

Has any one else noticed these?  Or know what they are all about?  Take a look on your train and let us know. xx