It's quite interesting, and so very unacceptable - in London, at least - to look at people taking the underground.
(By the way, it's still quite fascinating for me that large part of the underground is actually over the ground, while a similarly significant part of overground tracks goes below the ground... Talking about names...)
It's a golden rule not to stare at people. At all.
I broke that rule this past weekend, when I was on a train a lot.
There seem to be few types of people traveling: the tourists, the workers, the wanderers.
Vast majority with their Meeee-phones (me included:), glued to their screens; playing games, watching movies, reading, staring at some photos they took, or got.
Some are different. So much in the train and not in the train at the same time. In their own world, overwhelmed by their deep thoughts. Clearly in the middle of something happening in their lives. Not necessarily happy, but not very sad either.
I'm with them, too.
(By the way, it's quite fascinating for me that large part of these thoughts about other people is actually a reflection of my own thoughts about me... Talking about assumptions...)