It is mostly known to be used by the New York City Police Department ( NYPD ) , the NYPD Transit Bureau ( which was called the New York City Transit Police ) and the NYPD Housing Bureau ( which was called the New York City Housing Authority Police Department ) and other law enforcement agencies when they are at work in New York City . It is mostly known to be used by the New York City Police Department ( NYPD ) , the NYPD Transit Bureau ( was called the New York City Transit Police ) and the NYPD Housing Bureau ( which was called the New York City Housing Authority Police Department ) among other law enforcement agencies when they are at work in New York City .