Valentinian I mintmark help - Sirmium?

Recently picked up a lot of harshly-cleaned Roman stuff, which I've been having fun trying to figure out. This Valentinian AE 3 is the nicest of the lot, and yet the mintmark has me stumped. I found a bunch of very helpful online help with LRB mintmarks, but the closest I came was Sirmium and it still doesn't quite match.

Mine starts with a dot A (or delta?) SI R(?) B(M?).

Can anyone steer me in the right direction? My attempt at attribution is below.





Valentinian I Æ 3 (Æ 19)
(364 A.D.)
Sirmium mint
DN VALENTINIANVS PF AVG draped, cuirassed bust right / SECVRITAS REIPVBLICAE, Victory walking left, holding wreath & palm. ASIRM in ex.
RIC IX Sirmium 7a var (officina);
Sear 19512; Berthod 817.
(2.31 grams / 19 mm)

 

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Looks like this to me:
http://www.wildwinds.com/coins/ric/valentinian_I/_sirmium_RIC_007a_A.jpg
Valentinian I, AE3 of Sirmium.
AD 367-375.
DN VALENTINI-ANVS PF AVG, pearl diademed, draped, cuirassed bust right
SECVRITAS-REIPVBLICAE, Victory walking left, holding wreath and palm branch. Mintmark ASIRM.
RIC IX Sirmium 7a var (officina); Sear 19512; Berthod 817; NBD 11570.

 

As you noted,there is a • in front of the mintmark. It is from Siscia

•ASISC

 

Thank you both for your assistance, furryfrog02 and Victor. I appreciate it.

 

I've not seen a Siscia that looks like yours. That being said, I'm fairly new to this so I would defer to @Victor_Clark

 

Yeah, I am a little puzzled - the lettering is kind of mushy/blundered on mine, so it doesn't look much like the "dot ΔSISC," but that dot (which is quite clear) seems to keep it out of Sirmium.

This is my very first Valentinian I, so I am really new to this! I do appreciate your (and Victor's) efforts to help me out.