1. By "authorized by law" as an exception to the "no guns" signage, they mean cops, agents/employees of the state acting in an official capacity, etc.
2. Not familiar with the "30.06" sign designation, sorry.
3. The Castle Doctrine bill was signed and is supposed to take effect on or about September 8th, this year.
As for the criminals targeting your house for guns thing, I am far more convinced of that than that people will grab guns from OCers. Having had my dad's house burglarized and family guns stolen, maybe I'm just more sensitive, but if you leave them unsecured, you're asking for trouble. JMO.