It shall be unlawful for any person to construct or maintain any stairway, open cellarway, open basement way, or open entrance thereto in or adjacent to any sidewalk, pavement or street, and any such entrance is hereby declared to be a public nuisance; except that, all existing stairways, open cellarways, open basement ways or open entrances thereto in or adjacent to sidewalks, pavements or streets may be permitted to remain from and after the adoption of this prohibition if the person owning or using the opening in the sidewalk, pavement or street satisfies the Overseer of Streets that the opening is properly protected by a balustrade, or coping of durable material, and furnishes the city with a bond in the amount set by the City Council for the benefit of any person who might suffer an injury or damage by reason of the use of the stairway, cellarway, basement way or entrance.