The director, division of traffic engineering, is hereby authorized and directed to determine exact locations and lengths and to establish loading zones as defined in section 18-1(12), and shall place and maintain appropriate signs indicating the same and stating the hours during which the provisions of sections 18-133 and 18-135 through 18-140 are applicable. The director, division of traffic engineering shall have the power to issue or refuse permits for such loading zones and in deciding all such applications shall consider primarily the relationship of the loadings zones applied for and the public safety and convenience. No person other than authorized by the director, division of traffic engineering shall erect any such sign or place any such marking.