Short answers, pulled from the story.
The hand-in-waistcoat gesture, when used in 18th and 19th century portraiture, signified calm and firm leadership. An early 18th-century guide on genteel behavior described it as denoting "manly boldness tempered with modesty." It was also used as a sign that the sitter belonged to the upper class.
Napoleon's artist Jacques-Louis David used the hand-in-waistcoat gesture in several portraits of Napoleon, including the 1812 painting Napoleon in His Study. Because David was Napoleon's designated artist and the paintings were widely seen, the pose became closely identified with Napoleon even though it had existed since at least the 1750s.
The pose appeared in portraiture by the 1750s. Its roots trace back further to classical antiquity, when the Greek rhetorician Aeschines argued that keeping the arm close to the body, rather than extended outside the chiton, was proper form.
In mid-19th century photography, the pose may have served a practical purpose: tucking a hand inside a jacket kept it still, reducing the risk of blur during long exposures. The gesture is commonly seen in American Civil War photographs of military personnel.
Yes. The hand-in-waistcoat is a gesture recognized within Freemasonry. It appears in both Masonic contexts and in the broader tradition of European and American portraiture, showing that a single pose can carry distinct meanings across different communities.
Most paintings and photographs show the right hand inserted into the waistcoat or jacket. Some sitters, however, appear with the left hand inserted instead, so the convention was not strictly fixed.