Oddly, my friend who lives in a "good neighborhood" and frequently hosts gatherings of members of the bonsai club, has been written up in the newspaper as a local bonsai artist, they have had several major thefts over roughly the same 30 year period. Thieves each time targeted some of the best trees.
If you are going to have theft, it is not the unknown, stranger, druggies or whatever. Most likely it will be someone that you invited into your home specifically to see your bonsai. My friend who was ripped off a number of years ago, had the theft happen about 2 weeks after an "open house" for bonsai friends.