SmartWater is a proprietary forensic asset marking system that is applied to personal, commercial, and industrial items of value to deter theft and to identify culprits for prosecution. The non-hazardous liquid leaves a long-lasting and unique identifier that is invisible to the naked eye except under an ultraviolet black light.
Its use is described at The Telegraph:
Brent Police have recently been working with SmartWater using trap cars and houses equipped with technology to deter thieves from committing crime and to catch those that do.The company's website is here.
Residents have also been provided with free kits to mark valuable property with the substance within their homes which has led to reductions in burglary and street robbery and 80 and 40 percent respectively.