Police Officers are not course monitors.
At a road race, the role of the police officers is to manage the safety at road intersections. That is, to make sure runners do not get injured or worse from car traffic. As a race director you should never assume the police are familiar with YOUR road race course and will instruct the runners as to which direction to run. At critical intersections you must also place a knowledgeable course monitor to ensure that the runners follow the course correctly. That way your runners do not get lost and they stay safe.