The additional panels specify the meaning of the sign they supplement. Their nomenclature and meaning are the following:
S-800. Distance to the beginning of the danger or limitation. Indicates the distance from the place where the sign is to the place where the danger begins or the limitation of that one begins to govern. If it is placed under the hazard warning sign due to road narrowing, it may indicate the free width of said narrowing.
S-810. Length of the dangerous section or subject to limitation. Indicates the length of the danger or limitation.
S-820 and S-821.Extension of the prohibition, on one side. Placed under a prohibition sign, it indicates the distance in which this prohibition applies in the direction of the arrow.
S-830. Extension of the prohibition, on both sides. Placed under a prohibition sign, it indicates the distances in which this prohibition applies in each direction indicated by the arrows.
S-840. Warning for mandatory stop. Placed under the give way sign, it indicates the distance to which the mandatory stop sign at the next intersection is located.
S-850 to S-853.Priority route. Additional panel of R-3 sign, which indicates the route with priority.
S-860. Generic. Panel for any other clarification or delimitation of the sign or traffic light under which it is placed.
S-870. Application of signage. It indicates, under the prohibition or limitation sign that the sign refers exclusively to the output branch whose direction coincides approximately with that of the arrow. Placed under another sign, it indicates that it only applies to the output branch.
S-880. Application of signage to certain vehicles. It indicates, under the corresponding vertical sign, that the sign refers exclusively to the vehicles that appear on the panel, and that they can be trucks, vehicles with trailers, buses or cycles.
S-890. Complementary panel of a vertical sign. Indicates, under another vertical sign, that this refers to the circumstances that are indicated in the panel such as snow, rain or fog.