Exactly what my friends at church said.
I went to a rally a couple of years ago and spotted what I thought was a LE officer, he was obviously checking the crowd not the speakers..i walked up to him and asked what agency he was with..I said I was undercover also(i did not say undercover what!) . He tried to deny it and hurridly walked off. I wont describe the other tell here but its a pretty good one and not a weapon, experienced undercover agents know better, he didn’t.