Markings in the Overview section of the route inspector choose where labels sit along your route on the map:
The same menu sets what a label contains: Direction arrow, Segment length, Cumulative length and Hiking symbol. Choices that make no sense for the selected type are greyed out. The menu also sets the distance unit, and Reset to defaults goes back to the standard set.
The type of marking is saved with the route. A route you never changed follows the default of its activity. What the labels show and the unit are saved per activity, so they apply to every route of that activity and on all your devices. The route editor keeps its own choice, suited to planning.