Monitors

The first temperature and relative humidity monitor I noticed
was in a building on D.'s campus, which didn't strike me as odd.

I saw another in the Maritime Museum.

There is one near the check-out counter at the library.

There is one in the mall (photo taken in December).

This one is by the entrance to the grocery store.
Usually it is a much lower temperature.

Do buildings in the US have these, too, but not publicly displayed?  Is it required here?  What do they do with the information?

At least I have the answer to one question. What is relative humidity?  It is "the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature".