Fashionable pose for portraits back in the day. Old uniforms didn't have the same kind of pockets we have now, so while standing still for ages (while getting a portrait painted), you didn't have many other places to keep you hands, so unless you were brandishing a cane, scepter, or a rifle or something, it was an easy and comfortable pose.

I'm pretty sure i read somewhere that these old coats had pockets on the inside of the coat too, so technically the hand could be in a pocket. Maybe. As for why people back in "the olden days" sometimes put their hands inside their coat rather than in the outside pockets, idk maybe it's warmer because of body heat? No idea. Just speculating.

He also tied an onion to his belt, which was the style at the time.

tt30, ready to draw haha