Final answer:
Caution signals should be secured to the left side when the motorman's cab is on the right to ensure visibility to oncoming traffic and personnel.
Step-by-step explanation:
Since the motorman's cab is on the right-hand side, caution signals should be secured to the left side. This is so that the signals are clearly visible to oncoming traffic or personnel on the side that is not obstructed by the motorman's position.
Positioning safety signals on the left ensures that they are in the line of sight for those who need to be aware of the train's movements and any caution that needs to be taken.