Mint Mark on Constantius Gallus

[lawrence c]

I recently got this Constantius Gallus AE at auction. I have a question about the mintmark. On this coin it is "AMBI", which would seem to be Ambianum. The only mintmarks I see in RIC VIII, p. 124 (1981 ed) for this type is AMB. RIC lists AMBI for a Magnentius type, but not for this one. Is anyone else familiar with the AMBI for the fallen horseman type? Thanks much.
Best,
Larry 

[Pekka K]

As BI = 12 is number of workshop, this points to a large mint.

So the first 2 letters are "AN" for Antioch, and the coin is listed

RIC VIII Antioch 134: http://numismatics.org/ocre/id/ric.8.anch.134

Pekka K