It is unlawful to march in any parade upon any street unless there is carried unfurled at the head of such parade a flag of the United States of America, not less than 52 inches by 66 inches; provided, however, that this requirement shall not apply in case of a parade by any military or naval force of a friendly nation, who, as visitors or guests, may parade with their own national flag, colors or ensigns. (1961 code § 11.24.050.)