In heraldry, the drum usually signifies martial readiness, discipline, public duty, and the power to summon or command. Unlike animals or flowers, it is an inanimate charge whose meaning comes from social use rather than natural character. A drum calls people to attention, sets marching order, and marks ceremony, so it naturally came to suggest organized strength, resolve, and service under authority. It can also imply proclamation, reputation, and the ability to make one’s presence felt, which makes it especially suitable for military, civic, or institutional arms.
As a heraldic charge, the drum is a recognized but relatively uncommon device, which often gives it a distinctive and memorable quality. Traditional sources treat the ordinary drum as a side drum or field drum, and note that it is commonly shown palewise, with the drumhead to chief. Related forms such as the tabor, tambour, timbrel, kettle drum, and even the dumbeg may also appear when specifically blazoned. Because the charge is so strongly associated with procession, warfare, and ceremony, it often carries a tone of organized action rather than mere noise or entertainment. A useful historical example comes from the canting arms of Jehan Tabourot, noted by Mistholme, while later heraldic usage includes a range of civic and military bearings.
For heraldic reference, see Mistholme: Drum and Traceable Heraldic Art: Drum, both of which explain standard heraldic forms and variants. For image collections and real examples, browse Wikimedia Commons: Drums in heraldry and Heraldry of the World: Category: Drums. For useful background on the broader heraldic idea of object charges, Wikipedia: Charge (heraldry) is also helpful. Together, these sources show the drum as a heraldic emblem of command, order, ceremony, and steadfast service.