It's a traditional Spanish spade bit. I ride with them on my finished horses. It is the final step of the California Vaquero bridle horse process which consists of a bosal hackamore, two-rein (using the hackamore and Mona Lisa, half breed or salinas bit together) to finishing with a spade. It is purely a signal bit, used with rein chains. The horse works off movements in the rein and vibrations from the riders hands. Horse rides so light it's unbelievable. There is more information on this whole process in a thread in the Horse Training forum, called Old School Horse Training Approach if your super curious.
~Started young horses in Bosca te Ador, unto the two rein the old Spanish spade, brought them along with two hands that were gentle. Some fine reining horses as ever were made~