Nothing contained in this article shall prevent the erection of signs or structures over streets containing words or figures commemorating a historical, cultural, or artistic event or location in accordance with Section 67.29 hereof. Such signs or structures shall be erected, constructed and maintained in a safe and secure manner approved by the Board. All such signs or structures shall be constructed to withstand from any direction a wind pressure of 30 pounds per square foot of exposed surface. (Added by Ord. No. 135,775, Eff. 1/13/68.)