Snagg. RFID chips that you implant in your musical instrument as part of a theft deterrent system.
Their website explains how it works; click here to visit and read their FAQ.
Another reason to chip your instruments is that most insurance companies, whether specialty or home owners, will discount their rates if your instrument is chipped.
Realistically, the odds of getting your MI back after it has been stolen is probably slim but anything that improves the chances of recovery seems like a good idea.
Another good idea is to use Screaming Stone; click here to take advantage of their services.