The small plaque is representing a paramilitary man, with the same banded armour visible on the sarcophagus of the Diogmitas (paramilitary policeman) Aurelios Diodoros in Hierapolis. The man is advancing on horseback, brandishing a javelin. It is clear that this was the usual accoutrement for the local policemen or guards (fylakes).
Note the crested helmet of pseudo-attic typology