Hello? Equestrian = Longines, or Hermes.
Why does it have to be a pocket watch?
Longines of course as stated above are the official timekeeper of a bunch of equestrian events and have been since the late 1800s or early 1900s.
Furthermore, Hermes which is known for its leather saddlemaking craft has themed a number of wrist watches inspired by equestrian sports, including the watch called “Etrier” (stirrups) jointly produced with JLC, or the Hermes model called “Arceau” which features an asymetric design inspired by equestrian buckles,
Or the model called “sellier” which they created for a big anniversary, with a nail pattern again inspired by saddle making.
It so happens I have a couple such Hermes watches which I’ve been contemplating selling as I’m no longer wearing them so much, but I had not yet found the energy

Below is a “sellier” watch I already sold, and my “Arceau” watch which I still own.
Click to expand...