No person shall operate any crane, derrick, power shovel, drilling rig, hoisting equipment, or similar apparatus, any part of which is capable of lateral or swinging motion, unless there is posted and maintained in plain view of the operator thereof, a durable warning sign legible at twelve feet [3.66 meters] which reads: “Unlawful to operate this equipment within ten feet [3.05 meters] of high voltage lines”. Each day’s failure to post or maintain such signs shall constitute a separate violation.