Numbers shall be placed on existing buildings within twenty (20) days after the assigning of the proper number. The cost of the numbers shall be paid for by the property owner and the numbers used shall not be less than four (4”) inches in height and not less than half (0.5”) an inch in width and shall be made of a durable and clearly visible material. Numbers shall be conspicuously placed immediately above, on or at the side of the principal face or side of each building so that the number can be seen plainly from the street line. Only Arabic numbers shall be used. Roman numerals, script numerals or other types of numerals shall not be allowed. All commercial and industrial property shall have the numbers posted on both the mailbox and building so that the numbers are visible and identifiable at all times during daylight hours to persons in vehicles traveling on the street upon which the building is located. Commercial buildings with multiple occupants shall display visible business names and street numbers on back doors facing a public street providing access to the property.