Horn
The Cyclopedic Law Dictionary · Walter A. Shumaker and George Foster Longsdorf; ed. James C. Cahill · 1922
The Cyclopedic Law Dictionary
In old Scotch practice. A kind of trumpet used in denouncing contumacious persons, rebels, and outlaws, which was done with three blasts of the horn by the king's sergeant. This was called "putting to the horn," and the party so denounced was said to be "at the horn."
Bell, Diet.; Skene de Verb. Sign.; 1 Pitc. Crim. Tr. pt. 2, pp. 77, 80.