The City Hall Police are several officers assigned to escort the Ghostbusters to New York City Hall.
Primary Canon History
Once the Ghostbusters were freed from incarceration, they were escorted by several police officers to City Hall for a meeting with Mayor Lenny. As the Ghostbusters entered the building, the police held off reporters and photographers trying to get a scoop. In the Mayor's office, an officer was stationed for security purposes.
Secondary Canon History
One of the City Hall Police was assigned to the group that arrested Janine Melnitz's Ghostbusters team.