The custom of leaving rocks or pebbles on gravestones is an act of remembrance tied to the Jewish faith. The symbolic action indicates respect for the dead and serves as a sign that others have visited the deceased.
Judaism considers the marking of graves with stones to be a "mitzvah," or good deed. The practice likely began as a way to mark gravesites to keep the living from inadvertently bending or stepping over a grave. Today, the act is a symbolic display of respect and remembrance. The stone is always placed with the left hand, and it is left on the gravestone as a reminder of the lasting presence of the dead.