Who sits here
Usually, on public transportation, there are a few unwritten rules that everyone has to follow. One of them is that if you are a healthy young person you should give your spot to older people, the disabled, or pregnant women. It’s just the right thing to do and expected of you.
Some people don’t really care about giving up their seats for anyone, but in Japan, they have some that are designated for specific groups of people who should be sitting. The way they marked those chairs was by painting them with little stick people like that, just to make it obvious.