Signal systems for the starting and stopping of amusement devices shall be provided where the operator of the device does not have a clear view of the point at which passengers are loaded or unloaded. Any code of signals adopted shall be printed and kept posted at both the operator's and signalman's stations. All persons who may use these signals shall be carefully instructed in their use. Signals for the movement or operation of an amusement device shall not be given until all passengers and other persons who may be endangered are in a position of safety.