Some Frequently Asked Heraldic Questions
Simply put, a device says "this is me", while a badge says "this is mine".
Your device is your primary heraldry, what some call a "coat of arms" (more on that later). It's the design that signifies you; you have arrived at camp, you're coming into court, you're on the battlefield. It's the heraldry you wear on your surcoat, or fly as a banner, put on your shield or your seat or your dinner plate. This is the heraldry that allows people to find you.
Your badge is a sort of secondary heraldry, usually something far simpler that your device, such as a single drum or a cross. Like a "maker's mark", this is put on your stuff; your luggage, your mug, your kids, pets and gameboards. This is the heraldry on the items you leave around somewhere else, so that it can find its way back to you.
A "coat of arms", or simply "arms" is a device owned by someone who has been given the right to bear arms, granted by an Award of Arms or higher level award. Anyone can register a device with the College of Heralds, but you can only call it "arms" if you've received an award letting you do so.