When there is sufficient snow or ice to indicate that places designated under the provisions of this article may be used for coasting, the Mayor with the cooperation of the Police and Fire Departments shall prepare such places for coasting as provided by this article, placing Boy Scouts or such other assistants as may be selected to supervise and patrol the coasting thereon, and declare such places as ready and permissible for coasting. No coasting shall be permitted thereon until such precautions provided by this article shall have been carried out and until such places are properly marked and patrolled.