jim f:

Here is a more detailed regulatory example:

Canada OSHA (CANOSH), Part 14, Materials Handling (for federally regulated employer) Interpretation
14.1 In this Part, "signaller" means a person instructed by an employer to direct, by means of visual or auditory signals, the safe movement and operation of motorized materials handling equipment. (signaleur) Signals 14.25 No employer shall require an operator to operate motorized materials handling equipment unless the operator (a) is directed by a signaller; or (b) has an unobstructed view of the area in which the equipment is to be operated. 14.26 (1) Every employer who wishes to use signals to direct the movement of motorized materials handling equipment shall establish a single code of signals to be used by signallers in all of the employer's work places. (2) Subject to subsection (3), signals from the code referred to in subsection (1) shall be given by a signaller, who may use only those signals. (3) A signal to stop given in an emergency by any person granted access to the work place by the employer shall be obeyed by an operator. (4) No signaller shall perform duties other than signalling while the motorized materials handling equipment under the signaller's direction is in operation. (5) Where any movement of motorized materials handling equipment that is directed by a signaller poses a risk to the safety of any person, the signaller shall not give the signal to move until that person is warned of, or protected from, the risk. (6) Where the operator of any motorized materials handling equipment does not understand a signal, the operator shall consider that signal to be a stop signal. 14.27 (1) Subject to subsection (2), where the use by a signaller of visual signals will not be an effective means of communication, the employer shall provide the signaller and the operator with a telephone, radio or other audible signalling device. (2) No radio transmitting equipment shall be used in a work place for the transmission of signals where such use may activate electric blasting equipment in that place. (3) Where a signalling device referred to in subsection (1) functions unreliably or improperly and the operation of any motorized materials handling equipment cannot be safely directed by another means of signalling, use of the motorized materials handling equipment shall be discontinued until the signalling device is repaired or replaced. (4) Where an employee finds a defect in radio transmitting signalling equipment that may render it unsafe for use, the employee shall report the defect to the employer as soon as possible.