Defensive seating can take many forms. From benches with centre bars or "armrests" to keep people from lying down to backless concrete blocks, street furniture is increasingly being designed to defend against unwanted behaviours such as loitering or sleeping in public.
"Ideally, sitting should be physically comfortable- benches with backrests, well-contoured chairs. It's more important, however, that it be socially comfortable. This means choice: sitting up front, in back, to the side, in the sun, in the shade, in groups, off alone." -- William H. Whyte, The Social Life of Small Urban Spaces, 1980