Other than destinations around junctions, SLOW (supplemented by ARAF in Wales) is the only white-painted word to appear with any frequency on the British road network. It's meaning is clear, but it is used in a variety of places.
SLOW is most commonly painted on the road in advance of a bend, or series of bends, or indeed on a short straighter section within a series of bends. It is an additional warning for drivers alongside any Bend Signs or Chevron signs that are mounted on the roadside. Other uses include in advance of a hidden dip, blind summit, or sudden narrowing in the road, particularly where a S2 road drops to single track.
The word SLOW is normally sized to fit within the width of the lane it applies to. However, on narrow, but nominally S2, roads it can be wider than half the road, and when paired with a similar SLOW for oncoming traffic this means that the two 'W's overlap in the centre of the road (not literally). On single track roads SLOW can still be painted, spanning the full width, or nearly the full width of the road, giving the impression of 'MOTS' being painted on the road for oncoming traffic!