Cynthia Littleton Business EditorA group of 200 top writers, producers and directors have signed an open letter backed by the Brady gun violence organization that includes a pledge to incorporate gun safety best practices into their shows and to scrutinize the use of firearms in storytellling.The list of signatories includes Shonda Rhimes, Bill Lawrence, Jimmy Kimmel and the “Jimmy Kimmel Live” writing staff, Michelle and Robert King, Judd Apatow, Steve Levitan, David Shore, Matt Nix, Dan Lin and Jenni Konner. The letter frames gun safety an urgent social issue for the industry to embrace, in the same way that intentional depictions of such topics as cigarette smoking, drunk driving, the use of seat belts, marriage equality and LGBT rights helped change cultural attitudes and save lives.