Did you know that some of those signs are used to guide truckers or construction heavy vehicles to a particular site from a major road?
For example, a whole new huge sewer system is being built in the middle of nowhere in readiness for a new housing estate and one of these signs, say the circle, directs all the construction traffic off the A1 and the drivers need only look out for the circle to get to the right place. No postcode for the satnav yet. Clever, innit?