Man leave it alone, I have a friend that leave's bikes all over the place and just hops on what ever one is close. Some of his stuff sits around for a month or two before he gets back on and rides it. You are not the bike athority, People can do what they like with their bikes. If anything call the cops and say you think it is abandoned and give them your name, But don't move it, that could just totaly screw up someones day.