I see a few issues here.
First keeping a vest or jacket or even one of those pull out sashes with police on it in the vehicle is good but your assumption should be that most likely you’re not gonna have time to access that in a real situation.
Second, if you have a down threat with a weapon in hand you shouldn’t be rushing up to remove it unless you have a cover officer or you’re putting a security/anchor shot in their head first.
Third unless you are in actual uniform or your marked vest I would not be messing with the suspect’s AR from an officer safety POV. Read what Glen Meyer wrote again about recognition and response in the primitive parts of the brain. He may be a hobbyist when it comes to guns but he is a real deal expert in his field of expertise.
Fourth, From a preservation of evidence crime scene point of you unless there is an articulable reason to clear the suspects weapon just leave it where it is.
Fifth - I don’t know if FLETC stop teaching this but “police “is the most clear concise and easily comprehend it thing you can say to identify yourself. Federal officer or XYZ agency it’s just not as immediate from a communications point of view.