Around my way there are many footpaths with many walkers. There are not many mtb'rs, I'm one of the few but recently every trail has become strewn with logs and braches bent low. So i remove them and continue on my merry way. Next ride the same logs are back on the trail obviously to stop bikers but not placed in any official capacity.
The antisocial hooligans on the trails are not the mtb riding community obviously, although this one will become mighty unsocial if he catches a log placer in the act