Down on the platform at Shinagawa Station you can find some interesting items to commemorate the zero kilomoter marker which shows the start of the Yamanote Line.
You can see slightly faded in the above mark, where it says Shinawagawa 1885 and Yamonote Line Zero Post. The white marker below is positioned just opposite the Yamanote Line tracks.
I asked one of the JR station guys where it was and he had to call someone to tell me. Looks like not everyone knows about this bit of Yamanote Line history.
Japan Post have put up a post box with a sense of humor. It is the ‘zero post’.