Cartier Santos Large, stainless case on a Cartier rubber strap with a signed buckle, with black bezel.
It went up in a bag, and didn't come back..
Serial no. is 164833HK
(might be MK; only picture I have of the back is slightly blurry, wouldn't you know..)
(postscript : and found again, in a drawer on a yacht. Can't begin to explain that.)