I think when you see someone wearing your letters who is more than likely not a Greek-- you let it go.
And then you go back to your chapter and remind members not to give away letter items to non-members or Goodwill. In the case of your house being broken into, there's little you can do except to take precautions like locking doors and setting alarms--- and making sure members keep their personal items safe.
And then maybe you hold a clothing drive and donate all that gently-used non-letter clothing to a local shelter.
