While it is the athlete's responsibility to know the course, it is still your responsibility to properly mark a course. Not only should the course markings work for the athlete, they should also work for the community where the event is happening. Course markings should be temporary, as using permanent markings for the course is one way to not be invited back, and can lead to a large sum of money on clean-up expenses.
To determine what needs to be marked, analyze the event from start to finish in order to determine what would be helpful to your participants and spectators. People traveling to the venue most of the time can follow the car ahead of them with four bikes on it, but marking the nearest large intersection(s) with event signage is professional, helpful, and appreciated. Parking and registration, or packet pick-up signs, should be displayed. If you are holding a cross-country event at a resort, there are many lodges and buildings that may be confusing if someone isn’t familiar with the layout. Having signs marking the route to packet pick-up also saves athletes time and stress prior to their race. Be sure to give spectators and racers an opportunity to look at a course map near registration as well.
Out on course, the following should be marked: turns, hazards, feed and tech zones, king of the mountain, intermediate sprints, distance to go, and medical stations.
For mountain bike events, there are specific course markings that are used by USA Cycling, UCI, and other international governing bodies (see USAC Rule 5B). These course markings should be arrows of a contrasting color on a white background on a sign of one by two feet minimally. They should mark which course to follow, curves, intersections, and warn of situations that are challenging. Marking an intersection should be done prior to the intersection, at the intersection, and after the intersection to confirm the course.
For a road race, the course, curves or turns, king of the mountain, feed zone, and intersections should be marked as well. The difference here is that most often road bikes travel faster than mountain bikes, so markings should be further away from the actual change in course than they would be on a mountain bike course. USA Cycling regulation 3A3 covers required distance signage:
In all road events, at a minimum a conspicuous marker shall denote the final kilometer. A panel shall indicate the final 200 meters from the finish. Panels including the following distances from the finish line: 500 m, 300 m, 150 m, 100 m, and 50 m are recommended.
Panels indicating the last 25, 20, 10, 5, 4, 3 and 2 km are recommended for all road races. In races ending on a circuit, only the last 3, 2 and 1 km are to be displayed.
Make sure they are placed in advance. It is important to also check with the permitting agencies who you are working with as to what their requirements for signage is.
In a cyclo-cross race, the equipment pit must be marked by a yellow flag at the beginning and end where the course is divided between the race and pit lanes. A start grid needs to be marked out for major events. This grid should be placed behind the start line and consist of eight lanes, 75 cm wide by 10 meters long and used to organize riders for the start (rule 4B).