Tailors of Distinction - Whether they are are functional or not, a suit jacket will have buttons on the sleeve. A suit jacket with sleeve buttons that come undone (surgeons cuffs) is
Suit Jacket Sleeve Buttons: Numbers and Styles - Suits Expert
The Sometimes, Always, Never 3-Button Suit Rule | The Art of Manliness
Suit Buttons: Everything You Need to Know - Hockerty