There are actual faction of them (the scalphunters and random Bandas), and any party deserter party counting an important number of soldiers from the Mexico faction or the Bandas fits this trope.
Some hired guns and companions (Norm Finkleton, Hickory Jim, Oscar Harrison) start with one, and the outlaw Remington Robert (playable character in quick battle) too.
Badass Longcoat: It is one of the armours.
State militiamen, Pinkerton agents, Jackie Luong, and Charles Huntington wear one.
Badass in a Nice Suit: A few armours are nice suits.
Carl Brine starts the game while wearing one.
Badass Bandolier: A decorative feature on a couple of armours.