Your coin is a maiorina of Magnentius with the GLORIA ROMANORVM reverse type. The figure of the horseman carries no shield and is not nimbate. The victim kneels on one knee, and there is a broken spear and shield beneath horse.
This type was not used at Ambianum.
The mint mark is only partially on the flan, but appears to end in ..VS<dot> or ..VG<dot>. I find no attested mint mark with these or an LVG. combination.
I am not convinced I am reconstructing the mark very well. Here is the best blowup I can give for the present resolution of the original:

The obverse has an A in the left field behind the head.

Edited by lrbguy
03/03/2017 12:50 am