Howard,
Back when I first joined the board the situation you metion came up and I commented on our training
http://www.professionalsoldiers.com/...t=23932&page=3
I suspect that DEA still teaches this subject, a lot. BATFE, also.
I don't know whether or not they consider their POIs "law enforcement sensitive" but a FOIA may work? Otherwise, a recent grad of either school should be able to share current doctrine. I no longer have my materials to offer - and my mind isn't what it used to be.
Unless u/c, when in street clothes always have a badge affixed on your belt next to your holster, if wearing a fanny pack, have a badge sewn into the flap so it will be displayed when you remove your weapon, and always ID yourself verbally. If you are making an arrest while in civilian clothes, have your badge/creds in your "weak" hand and ready to "flash to the rear" in the event challenged. Never turn quickly towards the challenging officer and always verbally advise him/her of your intended movements.
Years ago, most major cities had a "color of the day" you displayed by wearing a hat/piece of clothing just before making an arrest in civilian clothes. One technique was to tell the challenging officer, I'm getting my (color) armband out of my right rear pocket and await his OK. It was a little safer than quickly pointing something shiny in the officers direction.
The challenging officer is amped up and no need to cause him to discharge on you.
If the challenging officer demands you drop your weapon after you have identified yourself, tell him you are going to remain in position and ask him to pitch a badge, ID forward.
Verbally sort of "feel each other out" with words such as, "If you are really a cop then you will understand ....." You don't want to give up your weapon if you are not sure - but you got to balance that with not getting shot by somebody just trying to do his job.
v/r
phil
P.S. Just as when one deploys to a foreign country, you got to "feel out the locals" when you come TDY to a different town. Different places have local recognition techniques that work and you need to know them for survival.