When I lived in London, I once came across a criminal operation that was producing fake documents, in what looked like substantial quantities. British & foreign driving licences, National Insurance cards, passports, ID cards etc. Not especially high-quality, but still.

Try as I might, I could not get the Metropolitain Police interested. From Royal Mail tracking numbers, I was able to figure out which post office the docs were being sent from. I took a pile of those fake docs to a large police station literally across the street from the post office. Got a crime reference number and was told to keep the docs. :)

In Zürich, I once came off my bicycle. No one else involved, no damage to anything except myself. The police were on the scene six minutes later (they responded when a helpful passer-by called for an ambulance). Offered to take my bicycle for safekeeping while I was in hospital, which was jolly nice of them. :)