White circles, squares, etc. on roads.?

Question

For years I have been trying to find out what the white circles, squares and triangles you see painted on most of the major roads in the UK mean. They are probably about 15 inches in diameter and I think they must be for HGV drivers, but what on earth do they mean?

Also, I often see two smaller white circles close together, rather like a colon sign on the roads. Does anyone know what these are there for please?

Answer 1

The answer above is wrong. you mean route markers, if you look at the road signs they will also have the same symbols and it helps motorists follow routes. they normally appear on roadsigns as a black symbol, as you say a diamond shape, circle, square etc. in a yellow box alongside the road number.

Answer 2

police use them for speed traps

they know how far apart they are and know how long it should take you to cross them, police can sit far away and see how fast you are going,

ps, on some motorways they have marks on the road and tell you to keep 2 marks apart from the car in front for safety