A colleague at work was talking about the Boss's new coat and remarking on how long it was (the coat was full length, right down to the floor). My colleague then said that he looked like a Pinkerton Agent. My question is... what is a Pinkerton Agent and what is the connection with the coat. Cheers.
Pinkerton's were the original private detective agency - in the USA in the late 1800s. Their logo was a wide-awake eye; hence the term Private Eye. I'm not sure that they wore long coats, but I suppose they might have if their ankles were feeling cold.
Since about the 1930s, it has been a TV, movie and comic book stereotype to show a private eye or detective wearing a long trench coat. Even Dick Tracy wore one, I believe.