Not Morse code at all. If you look at the parts of the train that touch the overhead electric cable (whatever they're called), there are two of them per carriage (which the artist forget to draw in). The Morse-like "dots" are the doors, the "dashes" are the passenger windows, the extra "dot" at the end of the train (regardless of the train's direction) is the engineer's cabin.
To anyone who hasn't read the tags, I think the [when you see it] is referring to the [underwear] at the front left which at first resembles a [rock].
