Numerals indicating the official numbers for each principal building or for each separate entrance, as specified above, shall be posted in a manner as to be visible from the street on which the property is located. Whenever any building is situated more than 20 feet from the edge of the street or road serving the building, the number shall, in addition to the other requirements of this chapter, be displayed on a post or other structure clearly visible from the street and stationed on the same side of the street as the building or premises for which it is intended. Said post, gate, fence, tree or other appropriate place shall be at least four feet in height and not exceed eight feet in height and shall be displayed in a prominent and conspicuous place in such manner as to be plainly legible and visible from the center of the street and easily discernible when traveling in either direction on the street so as to show clearly, if not otherwise evident, which is the driveway for the property. The numbers shall not be less than four inches in height and shall be made of a durable and clearly visible reflective material. The color of said numbers shall be in sharp contrast to the color of their background, and these conditions shall apply both to the numerals placed upon the building as well as numerals placed on any post, mailbox, gate, fence, etc.