If I felt that I was a target for a kidnapping, I would wear an implantable gps device and give access to my friends, family and colleagues.
that's probably how the US will push/justify the RFID chip on every human being.
I think plenty of criminals forget the fiat element though. You may end up with thousands of coins, turning them into cash if you have that need will become ever trickier under the radar. If and when the need for conversion is gone then things may get heavier.
If there is no need for conversion then this won't be an issue. If there is a need for conversion then think of the following scenario.
1. find a billionaire
2. steal his cat
3. announce that you will give them the GPS coordinates when 1 BTC reaches 100 000$ on all major exchanges.
4. the billionaire will move the market
5. all bitcoin sellers will become criminals during that period of time
6. the real criminal will sell a couple of hundred of bitcoins and lives happily ever after
the latter is possible during the times when bitcoin has a market cap smaller than the billionaire's wallet