Any person desiring to erect or maintain any blinker light or lights upon or adjacent to any street so located as to be visible from any street shall first make application in writing so to do to the City Engineer, which application shall state the proposed location of such light or lights, and a brief description of the proposed light or lights. The City Engineer shall consider every such application, and if it finds that the blinker light or lights proposed to be erected will serve as a warning to persons using the street and will tend to increase the safety of the traveling public, shall issue a permit in writing authorizing the erection and maintenance of such blinker lights. Such permit shall be valid until revoked and no charge shall be made for any such permit.