My only suggestion for this scenario, is anticipation.
In the past year I've noticed groups of boys eyeing me/my bike up, as I am approaching them, or going past. At first I thought nothing of it, and it was just curiosity. But after reading of bike-jackings, I realised that some of the kids might well want to relieve me of my bike.
Actually, they were only drawing up mental lists of all the things they wanted to relieve you of:
Actually, they were only drawing up mental lists of all the things they wanted to relieve you of:
:)