I remember that dude. The police got a call that someone was impersonating an officer. The ATF guy was there because they had reason to believe someone had a gun, likely owned by a criminal. He kept going on about some paperwork. There's no way to read paperwork that far away. As an ATF officer, he should have known basic police procedure. They're going to need to control the situation for their own safety because they have no idea what's going on. So you will be detained, and you will likely be cuffed. But if you are who you say you are, they will have no choice but to let you go, and they'll have egg on their face while they do it. Or, you can do this, and we can continue laughing about it half a decade after it happened.