Maximian, 286 - 305, 306 - 308, and 310 A.D.
This obverse legend / mintmark combination is not noted in RIC. Scarce bust type.
. Bronze antoninianus, RIC V 580/581 var, VF, Siscia mint, 3.97g, 24.8mm, 0°, 285 - 286 A.D.; obverse IMP C M A VAL MAXIMIANVS AVG, radiate bare bust right, from behind; reverse CONSERVATOR AVGG, Maximian, holding scepter, stading right and Hercules, resting left on club, standing left, sacrificing over altar, A in left field, XXIHP in ex; rare