People are entitled to do this though. As a matter of fact, the owner of the bike might lose it precisely because of you: he comes out right after you went in to notify the mall security, sees no bike around, assumes it's been stolen and walks away... Or he just comes out later, doesn't see his bike, doesn't see the note you've written (or it's blown away) - same thing... Honestly, if I ever come out of a mall and don't see my bike where I left it - I'll think of contacting Sherlock Holmes before contacting the mall security.