This is a manners poster. A what!? Yes, I understand your reaction. It is probably much like those punctuation marks. !?
You may have heard that Japanese people are so well-mannered. So polite. Etc. Well if that was true, there would be no need for these kinds of manner posters all over the subway.
This particular poster annoys me more than most. The question it asks in Japanese is "Why are your legs spread?" You may not be as quick as me to notice, but that's a man sitting there. A MAN.
Question answered.