I've gone out and asked an actual racer about this one.
There are usually some visual cues. The course is laid out in cones, the flags are asymmetrical so you know on which side you should pass, the gates you must fly twice through usually have something (bright fabric, a flag, ...) next to them on the side that you fly around before going back into the gate, etc. and the cones themselves are not just a flat string but are laid out in certain patterns; for example, when the sequence of cones terminates in an arrow this usually indicates you should go upwards (or higher, i.e. in the case of two gates stacked on top of each other), while a perpendicular line marks the entry point of the cone string.
Sometimes the track elements are colored differently (and asymmetrically) to indicate the direction. Some elements just have canonical uses based on their shape: you should pass through gates, fly besides flags, dive the dive gates... The Jacob's ladder specifically is almost always passed top to bottom in sequence (while whether you should go right or left varies track to track).
That said, there is no universally accepted, set-in-stone standard for these cues. Which ones are used depends a lot on the materials available to the race organizers, how much time they have to set up the track, the track's layout, etc. For instance, flags can either be fabric on a springy pole (in which case you fly on the convex side), or they can be inflatable and curved to hang over the ground (in which case you fly under the overhang on the concave side).
Most drone racing leagues have their own standard of how different track elements and maneuvers should be marked on the racetrack and try to stick to it. Even then some smaller local or regional events of the league may be limited by the organizers not having all the required materials. Also, one cannot mark everything on the more complicated, technical tracks, or mark it in an unambiguous manner. Sometimes some parts of the track are formed by the terrain itself, i.e. an abandoned building or natural rock formation. In that case there's no standard and the track designers must get creative to even make it clear where the gates are!
So visual cues aren't everything. A lot of races rely on communicating to pilots how the track should be flown before the race. Sometimes it's a verbal briefing, sometimes a printed schematic. Sometimes the track is published well in advance so pilots could train on their home field or in a simulator. There could even be a video walkthrough or a DVR of a practice run. Additionally, many leagues actually perform a physical walk through of the track on or before race day (much like Formula 1 car racing), so that the marshals and pilots can discuss challenges, specific items and hazards, etc.
In the end, for serious racing, how the track itself is marked does not matter. During the actual race the speed at which everything is happening does not leave you any time to think or figure out what's coming next by parsing the track. The racer just knows in advance which gate or maneuver comes after the one he's flying through, and anticipates it, most likely along with the one after that as well. Knowing the track is a very important factor in winning a race, as in order to have the fastest (which usually means shortest) trajectory, the pilot must start the necessary maneuvers for passing the next gate while he has not yet passed the previous one.
Besides training beforehand and learning the track from the given materials, the racers are always allowed to fly some laps around the actual final track before the race in order to memorize its layout. This is critical as the actual racetrack will always slightly differ from whatever training track they might have constructed for themselves. During these training laps they also figure out the best way to tackle the elements of that particular track in the speediest way possible, and thus develop an optimal trajectory, or racing line, as it's usually called.
So, in the end, the on-track markings are there just to aid in the initial few laps as the track is being learned by the pilot, and after that, memory takes over.