Helena AE Follis, 3.15g; 21mm, 326-327 AD. Arles. 

Obv: FL HELENA-AVGVSTA, diademed and draped bust right
Rev: SECVRITAS-REIPVBLICE, Securitas standing left, holding branch

S-F across fields
Mintmark ARLT. 

RIC VII Arles 317. Very Rare (R3).

With permission of Roma Numismatics, December, 2009