Bruce Schneier point out the fatal flaw in "SmartWater," an invisible, tagged paint you daub on your possessions so they can be traced to you if they've been stolen:
…An additional feature of SmartWater Instant is the inclusion tiny micro-dot particles which enable Police to quickly identify the true owner of the property.
The idea is for me to paint this stuff on my valuables as proof of ownership. I think a better idea would be for me to paint it on your valuables, and then call the police.