Had a look into what it was and to my surprise it was an official certificate for passengers to show to their boss as proof that the train was late.
These days, the "late-train-certificates" are issued online
like this one which proves that the Chuo line was running 10 mins late between the hours of 7 and 9AM. The photo of a poster above informs passengers that they can get their certificates online.
This page at JR shows which of their lines are running late and by how many minutes.