Practical things you can do:
1- Change the name on the transom, and change the colors fo some trim and the sail cover.
If someone has a grudsge against the past owner, this may give them a hint "It ain't his boat any more!". Changing marinas would also help that.
2- Spend some money on security. Put in a cheap car alarm with a trigger switch tied ot the dock, so if it is cut free an alarm will go off. You can add a pressure mat in the cockpit or other sensors to go off if someone boards, this ain't rocket science.
3- Add a GPS tracker, like a Zoombak or Blackstone Harpoon or Entourage (aka Passport) or similar. Available from Escort (Cincinatti Microwave) and Radio Shack or directly online. Not cheap, about $150 plus that much again annually but it will track your boat and can alert you if the boat leaves the dock without you.