The following shall be authorized for nonresidential establishments in all districts: One temporary sign no greater than 12 square feet in sign area may be displayed for a period not more than 30 days after the opening of an establishment nor 30 days before; one temporary sign, no greater than 30 square feet, advertising an on-site promotional event for an establishment and may be placed at a establishment two times per year, not to exceed 30 days each time except that such may not be used simultaneously with a sandwich board sign as authorized by Chapter 208, Signs; temporary window signs may have a total combined sign area of no more than four square feet; temporary signs shall not include pennants, flags as not otherwise authorized, and any suspended or attached pennant that blows in the wind or a spinner which spins in the wind.