I know it's important to ID and warn before shooting--but I believe a moment's hesitation, along with the ruthless nature of these gangs--and you are likely going to be dead.
Reminds me of a quote from one of Jim Cirillo's books. He was questioned by a lieutenant after a shooting as to whether he had identified himself as a police officer. "Yes, but I don't think they heard me over all the shooting."
Sometimes things happen fast. When it's time to shoot, don't talk. Shoot. Otherwise, you might end up like that guy in the Burger King in Miami a couple of years ago. Or worse.