The length of road to which a traffic sign on a road (except a parking control sign) applies is worked out in the direction driven by a driver, or travelled by a pedestrian, on the road who faces the sign before passing it.
Example
Rule 21(3) provides that a speed-limit sign applies to the length of road beginning at the sign and ending at the nearest of a different speed-limit sign , an end speed-limit sign , or speed derestriction sign , and the end of the road. Only the nearest of those things, in the direction driven by a driver, or travelled by a pedestrian, who faces the sign before passing it, is relevant.
Notes
1 Parking control sign and traffic sign are defined in the dictionary.
2 Rule 332 deals with parking control signs that display an arrow. These signs apply to lengths of road.