Shield decorated with slow quadriga left, with emperor, or Sol.

It's perhaps difficult to determine from the detail as to which personage is represented, however S. Estiot suggests (p.c.) that the slow quadriga represents a processus consularis, and would thus imply the emperor. Whereas Sol's iconography would employ a galloping quadriga.

Cornelius Vermeule, in "The Imperial Shield as a mirror of Roman art on medallions and coins", citing a similar coin in the Ashmolean, also believes this to be Probus himself.

If so, this may be a reference to his second consulship.