Accident Black Spot
In general terms, an Accident Black Spot, also sometimes known as an Accident Hotspot or a Site for Concern, is a place which is perceived to have a higher than normal casualty rate. Highway engineers have access to the general accident data (known as STATS19) and can determine casualty reduction schemes from this information.
In the 1960s and 1970s, however, Central Government authorised use of a non-standard warning sign to denote an Accident Black Spot. The vast majority of these signs have since been removed either due to improved engineering on the roads in question or due to the introduction of alternative casualty reduction measures such as Safety Cameras or lining/signing schemes.
The cult 1980s film Withnail and I refers to these signs, suggesting they were caused by distressed pedestrians committing suicide.
Many modern equivalents have signs that say how many people were killed or seriously on that road in previous years, to warn drivers about the danger of the road. In particular, Cheshire has a series of roads designated as a Red Route (not to be confused with the parking control) - these relate to the risk severity of a given road.
In the mid 2010s, new signs denoting Accident Blackspots appeared in parts of rural Essex. Their legality is unknown as there are no records of a DfT authorisation for a non-prescribed traffic sign.