This very interesting Roman terracotta plaque has really unusual  iconography:  shows Dionysus on his panther, but the he looks more like Heracles with the lion-head cap, so it is a  syncretistic image, a combining of the two gods.

The inscription does indeed give the name of the god in Greek letters:  before the mouth of the panther: ΔΙ, then under the animal, upside down, in two lines: ΟΝΥ/ΣΟΣ, i. e. Dionysos. The meaning of the letters  in front  the god's head cannot yet be determined.

88mm.

Roman, 1st - 4th century.