John Riley "Jack" Duncan (September, 1850 - November 16, 1911) was a renowned Texas lawman with service as a Dallas police officer, Texas Ranger, and detective. His boot spur was rumored to have tracking powers imbued into it.
Tracks the movement of an object or person. Horses will be afraid of whoever touches the spur for a couple of days, however.
Brother Adrian used a fake copy of the original spur to trick Artie into destroying it, thus proving that Artie had something to do with the disappearance of the Astrolabe and its possible use.