Branding, an ancient mode of punishment by inflicting a mark on an offender with a hot iron. It is generally disused under the English civil law, but is a recognized punishment for some military offenses, as desertion. It is not, however, now done with a hot iron, but with ink, gunpowder, or some other preparation, so as to be visible, and not liable to be obliterated. The mark is the letter "D," not less than an inch in length, and is marked on the left side two inches below the armpit.
Entry from Everybody's Cyclopedia, 1912.