I have always called them election hoardings. When I was discussing the quality of said constructions this morning I got a blank look. Billboards I added and was understood. I have always thought of them as hoardings. Billboards populate desert landscapes for Wile E. Coyote to hide behind in order to ambush the Road Runner. I might be making that last bit up.
Anyhow the Greens win the contemporary look award. I think I saw somewhere they had flogged the idea from another Green party somewhere else on the planet. Whatever.