Preparations for the likely bombing of military installations, industrial facilities and civilian populations led to the creation of many thousands of temporary and permanent air raid shelters. For people caught outside when the siren sounded they were guided to the nearest shelter by the ubiquitous 'Shelter' signs. These would often convey the distance to the shelter in yards and also sometimes the number of people the shelter could accommodate. There were obviously many hundreds of thousands of these enamel signs manufactured. Some are double sided so they could be used from any direction. Following the war many would stay in situ for many years and others were removed and thrown away. Those that remain are highly collectable and can reach many hundreds of pounds at auction.
News about interesting insignia, ARP related info and period photos that turn up.