Possible Clues:

• Perhaps stop king doing as planned
• Traffic notice
• Source of information or instruction, by the way
• No overtaking, perhaps, as horseboxes like to hog lanes in the end
• Speed limit posting, e.g.
• It gives indication on routes, speed limits, potential hazards etc.
• So daring a change seen along the way
• A pointer along the way
• Roderick included a token, something that can be seen along the way
• Info for drivers