Constantine II, AE4, Siscia.

Obv: CONSTANTINVS IVN NOB C, laureate, cuirassed bust right
Rev: GLOR-IA EXERC-ITVS, two soldiers holding spears and 
shields with one standard between them. O on banners.

Mintmark: epsilon SIS star. 

RIC VII Siscia 262, rated R2.

From Dane's collection, August 2010.

Known mintmarks for this RIC number:
ASIS star
BSIS star
epsilon SIS star