Constantius II. 337-361 AD. Cyzicus.

FL IVL CONSTANTIVS NOB C, laureate, draped, cuirassed bust right
GLOR-IA EXERC-ITVS, two soldiers holding spears and shields with one standards between them, O on banners.
Mintmark: SMKS

RIC VII Cyzicus 126, rated R2

From Dane's collection, Feb. 2011.

Known mintmarks for RIC 126
SMKA  r2
SMKB  r4
SMK gamma r3
SMK delta  r2
SMK epsilon  r2
SMKS  r2