Only fools and horses

The funny thing is that this sign is on a residential road in the seaside City of Brighton & Hove which has a population of over a quarter of a million and extends over an area in excess of 30 square miles. I have lived here for a *very* long time - and I have only seen a horse in the city on two occasions - the first was in the late 1950's when the "rag and bone" man came round, and the last was when the police horses were out for a walk. I don't quite understand why this sign needs to refer to horses - was there once a problem with them grazing by the side of the road in the leafy suburbs? Does anyone else have signs like these?