This great vintage advertisement teaching subway etiquette is found in an old train at the New York Transit Museum. It was part of a series of similar signs under the name "The Subway Sun", each with similar tone and art. Alas, this problem still exists today, so don't be the guy/gal who blocks the door, or else you may get a purse to the head.
Subway Etiquette Tip #44: Don't Block the Door
Photo:
New York Transit Museum
Photo:
street moments