When is a pile of stones a work of art, a historical monument or an act of vandalism, and how much signage do we want in the Scottish Hills? David Lintern considers cairns, signposts, interpretation and other human interventions, both seen and unseen. A pile of rocks Cairns are perhaps the oldest marks in our landscape, but their existence is complex – they have different forms and functions. Some designate a summit or an ancient site, waymark a route, others seem to be more about mark making or decoration. Recently, Skye locals clubbed together to remove rock stacks made by…