In reply to SenzuBean:
> Put a bag of red ink in the pocket so that if gently disturbed it will spill everywhere. Then wait outside in a casual place. Eventually you will spot the thief and can then deliver the classic line "Aha! I've caught you red-handed"
Hmmm, got me thinking. An uninflated balloon with a small quantity of ink and a small length of tubing(about 2-3mm diameter) inserted and secured in the neck of the balloon(and an OLD pair of trousers).
Might actually be feasible
Post edited at 12:47