Found this and sounds quite "interesting"
Its a pen that will squirt dye onto a mugger (or anyone I suppose) so that if the police are involved, helps them identify the offender.
Sounds quite a good idea, plus its free. It does say if you order more they do discounts, but they will send one for free if you fill in the form.
You will need to put something in the comments box (Mr Un-Original here just put thankyou).