Last night I ran into all these Nitrogen tanks on the street! I was so confused-- and they're bigger than I am! Apparently they're from Verizon, who keep their underground cables pressurized to keep out moisture. I was hoping it had a more exciting explanation... Like belonging to a very eccentric yet easily amused professor who had a penchant for freezing things randomly and a (very poorly hidden) secret underground ice cream speakeasy for the hordes of rodents and mutant ninja turtles in the sewers.
Well, not everyone can live the dream.