Every neighborhood has a small police station (called a “koban”) – so there are lots of kobans. They are staffed by one or two policemen. Many are labelled with the English word “KOBAN” (as well as the Japanese word of course).
They are there to help (and keep an eye on) what happens locally. If you lose anything, go to the nearest koban to report it. (There’s a good chance the finder will return it to the koban – Japanese people are famously honest and helpful in returning lost property, even wallets full of cash)
Japan Tourist Tips 