Hermes belt, a subtle reminder of luxury. Too bad he's wearing a waistcoat over the belt - a big fashion no-no according to tradition.
"The purpose of the waistcoat is to create a flowing silhouette – if the waistcoat is in a different material then it still has this function but also sets off both jacket and trousers to great effect! Wearing a belt defeats the purpose – the bulge of a belt, or worse, the shine of its buckle, interrupts the flow of the material and makes something beautiful into something ugly. Traditionalists would argue that the trousers must be worn with braces, however this is only a good idea if you’re wearing high-waisted trousers which have brace-buttons – if not then you’re better off to just to leave them as you are. The most important thing to bear in mind is fluidity."
Also, the waistcoat should cover the shirt front. Exposing it like this means the vest is too short.