It shall be unlawful to erect any sign, or post supporting such sign, within the curb line of any sidewalk within the city or to permit any sign to project beyond the curb line of any such sidewalk into or over any portion of any street or to project over such sidewalk more than three feet (3') from any building to which it may be attached or to be so constructed that the lower edge thereof shall be less than seven feet (7') above the sidewalk level at the point where it is attached to such building without having first applied for and received a special permit from the city council. (Prior Code § 18-18)