they are indeed so helicopters can follow pipeline routes. Orange hats indicate major changes of direction in an underground gas pipeline. If it's white with a black stripe it's an oil pipeline. What this has to do with adverts, i'm not sure though...
both previous answers are correct. All over the uk there is a grid of pipelines feeding oil (kerosene) to our airports and raf stations.These orange posts guide a helicopter usually once a month the route of the under ground pipeline to allow the observer to check that ther are no unauthorised digging near the line and he can tell by the colour of the earth if there is a leak.