All members shall be placed in a conspicuous place, next to the street or avenue on which the house, building or place of business to be numbered shall have its main entrance (and in the case of houses, buildings or places of business facing upon alleys, the numbers shall be placed on the main entrance facing such alley) and the figure or figures of any such number (or letter) shall not be less than three inches in height; provided, that if the lot or piece of ground occupied by a single dwelling house is of sufficient width to require more than one number or shall be so situated as to be partially within two twenty-five foot number districts, it shall be sufficient to place on such dwelling house the number of the lot or twenty-five foot fraction on which the main front entrance is situated. (Prior code § 5-46).