All awnings hereafter erected shall be elevated at least eight feet, at the lowest part thereof, above the top of the sidewalk and shall not project over the sidewalk to exceed three-fourths (3/4) of the width thereof. They shall be supported without posts by iron brackets or by an iron frame work attached firmly to the building so as to leave the sidewalk wholly unobstructed thereby. All awnings heretofore erected in a different manner shall be removed within a reasonable time after notice hereafter as specified. If any person shall erect any awning contrary to the provisions hereof; or shall refuse or neglect forthwith to remove any awning or awning post after written notice to remove the same, to be given by the said engineer he shall be subject to a penalty of five dollars ($5.00) for each offense, and to a further penalty of five dollars ($5.00) for every day he shall fail to comply with such notice, after a lapse of five days from the service thereof.