There is adopted a uniform system of numbering all houses, store and other buildings (except shed, private garages and outbuildings) now erected or which may be erected within the corporate limits of the city, by placing on the door or door frame of the main entrance to such building, or on a conspicuous place nearby and conforming to such door or main entrance to such building and as near thereto as practicable, the number assigned thereto as provided in this chapter, such number to either be painted on the building, or on the glass or metal to be attached, or by he use of metal figures, at the option of the owner, and so placed as to be readily seen from the street. The figures so designating the number, whether painted or otherwise, shall not be less than two and one-half inches in length. (Ord. 1770 §1, 1928).