[nzjrs]

False positives and the human reaction to being accused of theft will kill these. Honestly a sticker that says "automated theft detection system in operation" will be more effective

[sippeangelo]

Works about as well as you'd expect: http://vm.tiktok.com/RWpGfb/

[caf]

A friendly animated cartoony robot face on the screen would probably be pretty effective.