Flags can be signs. Get over it. 

From the proposed Guidelines:

General. Subject to Sections 600.3, 600.4 and 600.5 below, all signs, billboards or advertising structures of any kind are prohibited except upon application to and written permission from the ARC. Flags that may constitute or be considered signs in the reasonably exercised discretion of the CPI Department, based on their content, how they are used, and how they are displayed, are governed and treated as signs under these Regulations.