Coin has seen better days, but I think it's a quite rare one w/ this bust type and obv legend from Trier.
CONSTANTINE II AE3 18mm 3g Follis/Nummus (F+, patina)
AV: CONSTANTINVS IVN N C; laureate draped cuirassed holding Victory on globe in r. hand and parazonium n l. arm bust l.
REV: VIRTVS EXERCIT; 2 captives on either side of banner inscribed w/ VOT/xx.
EXE: STR, Trier mint.
REF: RIC VII Trier 275, rated R5 (very rare) 320AD.
Didn't see another one for sale in my short survey. Not in the best of shape but I figure it's a quite rare one.