Within every publicly owned building open to the general public for the primary purpose of exhibiting any motion picture, stage drama, music recital, or any other performance, with the exception of any indoor sporting event, signs shall be posted in sufficient number and in locations as to be readily seen by persons within the area, that shall designate that the smoking of tobacco is prohibited in any area other than that commonly known as the lobby. This prohibition shall not apply except during those times when the building is actually open to the

public.