Signs or indicating lamps shall be placed at all switches in electric light and power plants or other places where high-pressure currents are used, to show whether the current is on or off the circuit. When current is turned off a circuit for repair, the switch shall first be tagged, the tag bearing the name of the person for whom it is turned off. The tag shall not be removed or the current turned on until the person for whom it was tagged shall notify the operator that his work has ceased.