Arming the private security guards

Do you believe the private security guards should be armed? Should they be trained in defensive tactics? Should private security be able to use identifying information which may be misleading to the public, giving the public the impression that they are law enforcement? Should law enforcement officers be allowed to work for private security when they are off duty? Do these situations provide a false sense of security for the public? Be sure to provide real life examples in your answer and be sure to cite your sources.