Here is a nice example of this rare type with an F between the standards.
Constantine I
A.D. 335-6
16x17mm 2.3gm
CONSTANTI-NVS MAX AVG; rosette-diademed, draped and cuirassed bust right.
GLOR-IA EXERC-ITVS; Two soldiers helmeted, stg. facing one another, reversed spear in outer hands, inner hands on shields resting on the ground; between them two standards with F between.
in ex. AQP
RIC VII Aquileia 131
