The trains in Tokyo have courtesy seats for the elderly, disabled/injured people, parents with babies or pregnant women. But it's not always easy to tell if a woman's pregnant. You don't want to embarrass someone who might just be a bit chubby by getting up and offering her your seat. Solution: pregnant woman can wear or attach to their handbags badges that look like the window sticker on the right. The Japanese means roughly, "There's a baby in my belly."
I've got a bit of a belly, so I am considering trying out one of these badges. Since I'm a guy, I'm not sure how well it would work. It'd be funny to see people's reactions, though.
In the meantime, I just walk around carrying a cane and sit wherever I like.