More posters on the Japanese underground trying to teach people good train manner.
Folks who have been to or live in Japan will notice that people generally dont carry around large baggage on the trains ad its considered rude.
I remember my wife bought a bicycle in Okachimachi and tried to bring it home on the train - the station bod didn't let her through the barriers. She ended up riding the bike from Okachimachi all the way to our apartment in West Tokyo.
Back in London, taking a bicycle on the trains was so normal that we thought it may be the same in Japan.
Are there regulations in your region regarding the size of items that are allowed to be carried on public transport?