That's something I would be very interested in!
What is the source/provenance of the photo above?
The strange thing about Senior's watch is that it seems to be different styles in different scenes.
As we know there are the ordinary open face pocket watches as seen above, and the "hunter case" watches.
With ordinary pocket watches the stem/winder is generally at 12 o'clock.
With Hunter Case watches the stem/winder is generally at 3 o'clock with the hinge at 9 o'clock.
So, in the biplane scene Senior pulls out his watch, the stem is at 12 o'clock and he looks at the face without having to open a cover, thus it's an ordinary open face watch.
But in the sidecar scene it's clearly a gold Hunter Case watch with the stem at 3 o'clock and the hinge at 9 o'clock and Connery flipping open the cover to see the face.
It's from another thread I started that someone named rene007 replied to with information about the watch (Click HERE)
He says it's taken from a book called, "From Star Wars to Indiana Jones - The Best out of the Lucas Film Archive - By Mark Cotta and SHINJI HATA". And yes, there appears to be two different watches. The full hunter is in that scene with the motorcycle. I don't know if it's the same brand or not. Indiana Jones is not known for consistency (there's two very different Staff of Ra medallions in Raiders for goodness sake and apparently they thought no one would notice).