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.
"Don't Throw Chewing Gum on the Platform" (1976)
"Don't Forget Your Umbrella" (1981)
"No Smoking During Non-Smoking Hours" (1980)