I went to the NYPD Museum in downtown Manhattan this past Friday. Imagine my surprise to have stumbled across the "Hall of Groggers." Apparently, the "Grogger Task Force" dates back to the days of Peter Stuyvesent, when the rattlers were the primary tool of law enforcement in New Amsterdam, and they persisted in New York for centuries.
From 1609 to 1664, eight Dutch colonists carried lanterns and wooden rattles as they watched over the streets of their colony. The rattles were pre-whistle noisemakers that would alert members of the community to crime, fires or other threatening situations. The lanterns the men carried were made of green glass—this helped identify them to citizens. The green light became synonymous with aide and assistance and to this day, green lights are lit outside the entrances to Police Precincts in homage to the men of the Rattle Watch and to reassure citizens that the police are on duty. It would be over 150 years before the NYPD was officially created, but many of the traditions started by the Rattle Watch remain today.
Additional true facts about the grogger and our noise-making tradition can be found here