Visitors to the gravesite leave some stones to indicate that someone has been there. It's a sign that that there is still someone around who remembers and cares and takes the time. The cemetery in which my own mother is buried is so well-manicured that I put stones >from my own backyard in my pocket before I make a cemetery visit. In a way that I can't quite explain, leaving the stones makes me feel as if I'm somehow also leaving a bit of myself and my abiding affection there between my visits. I often do the same when I visit non-Jewish graves.
