I have always thought radio-controlled small explosive charges would be effective deterrents to this kind of thing.
I think you a really on to something here. Police decoys could be carrying items in which are hidden small dye packs, much like the ones hidden in money handed over to bank robbers.
In the fall of 1975 five members of a pickpocket gang were injured when a stolen wallet exploded as they were splitting up the loot. I think the one holding it had his fingers blown off.
The Paris police were much more concerned about catching the wallet owner than they were about the thieves.