The term "red light district" is widely believed to have originated because of this object.
Window lamps
Railroad lanterns
Traffic signals
Matches
Railroad lanterns. The origin is uncertain, but is often credited to railroad workers leaving their red lanterns outside "houses of ill repute" while they visited inside, or perhaps with prostitutes using those lanterns to advertise their presence to railroad workers. The first known use of the term in the US was in the Milwaukee Sentinel, Sept. 10, 1894.