What is this?

 I was walking in my neighborhood in NY (Hell's Kitchen area) and saw this  large  square shaped thing that apparently was made of iron, maybe steel but was apparently  rusted.  I took a photo of it and a close up photo of the engraved letters on it. Maybe if you can look closely at the attached photo you can make out some of what it says. 

The thing had  on its upper right corner, a protrusion that essentially was like a part of a  plumbing pipe that had inner threads.

My best guess is that this is part of a boiler for a building.

Any engineers or building- maintenance workers who know what this is and can verify it?