Each passenger elevator in a permanent installation used by the public shall have a sign that reads “Warning - Elevators shall not be used in event of fire - Use marked exit stairways”. The sign described in subsection (a) of this section shall be posted: at the entrance to the elevator shaft on each floor; and directly above the call button. A sign similar to the sign described in subsection (a) of this section shall be posted within the elevator car. The top of each sign may not be more than 6 feet above the floor. The lettering in the word “warning” shall be at least three-eighths inch high and the rest of the lettering shall be at least one-fourth inch high.