Hoardings refers to a large board at the side of a road, used for displaying advertising posters. And Unipoles refers to larger advertising board on one single pole.
This is smaller version of Hoardings. But are in back sides of Road Signages. These tiny and cute little structures are besides roads, and have high amount of visibility among road side walkers.
Big over head panel hoarding on road is called as gantries. Because of its nature and location it has high amount of visibility.