From Pink Tentacle comes this colorful image, "Three Annoying Train Monsters," a vintage subway-etiquette poster from Tokyo that warns riders against becoming the "Nesshii (the sleeping monster), Asshii (the leg-crossing monster), [or] Shinbunshii (the newspaper-reading monster)."
I posted a few more below, but you really should visit Pink Tentacle for the entire collection of these vintage gems, which transform the practice of good manners into something truly spectacular.