Diagram 559 has 2 variations depending on where the danger could be present. Often used on hilly and mountainous areas that often has loose rocks or debris from cliff faces of steep hills next to the road.
Material: R2/RA2 reflective overlay on aluminium composite backing
14.1.1. The risk of falling or fallen rocks sign, diagram 559 (S2‑2‑44, see Figure 14-1), should be used where there is a danger of rocks falling onto a road. A plate, “For” and a distance, indicating the length of road likely to be affected may be used with the sign. The appropriate variant is used to indicate which side rocks might fall, but where rocks might fall from either side (e.g. in a gorge) the left hand side of the road variant should be used