Welcome to United Bimmer Phil.
This is the first time I have ever heard of someone wanting to steal the catalytic converter in a vehicle. I'm used to hearing about has being stolen but not a cat. Do the local police have a memo or bulletin about this? I'd ask if they do, and ask for a copy. I would show that to your insurance company so they know what's going on as well. One good thing to do is to identify your cat with a special mark of some kind. Maybe scratching the last 7 digits of your vin into it? But make sure to take a picture of the mark for your records and proof. That way if it is stolen your insurance company will already know about the local thefts and as well you can show them that you took steps to help identify yours in the event of a theft.