Valentinian I, AE3, Siscia. 367-375 AD.

DN VALENTINI-ANVS PF AVG, pearl diademed, draped, cuirassed 
bust right.
SECVRITAS-REIPVBLICAE, Victory advancing left, holding
 wreath and palm.

R over Symbol 4 in left field, S over dot in right field.
 
Mintmark: gamma SISCK.

RIC IX Siscia 15a, type xxxvii(d)

Courtesy of coins_to_medals on vcoins.com.