Yes, that.Announce your presence and inform the police that you are armed and place the firearm on the floor and back away from it with your arms extended.If you are a "good guy with a gun" and you see a cop, you immediately drop your weapon and put your hands up, immediately. That this escapes anyone is puzzling.Your premise is wrong at the most basic level. The correct mode of action for a CCW holder is to hold in place, and if the shooter tries to enter the area he controls, take him out.
Private CCW holders can be compared to a minefield, what you are hoping for is the active shooter doesn't expect armed resistance and the CCW holder can get some shots in before the active shooter realizes he is being confronted.
If you hold in place and you hear someone coming down a blind hallway, do you shout out and ask if they are the police, the shooter or another good guy? If it's the shooter, you're shit out of luck, aren't you? If it's the police they may not believe you are a good guy. They may think you're the shooter trying to save his sorry ass.
And if you hold in place but can hear the shooter actively killing people in another part of the building, what do you do? Your gun becomes a joke to the people who are dying.
So you should check YOUR premise for reality.