Constans (337-350 A.D.) - AE4 - 15.94mm, 1.71g
Obverse - CONSTANS-PF AVG
Constans, his laurel and rosette diademed, 
draped and cuirassed bust in paludamentum right.
Reverse - GLORI-A EXER-CITVS
Two helmeted soldiers standing facing, each holding an inverted spear,
and leaning on a shield, one standard between them.
SMTSΓ in Exergue. O in standard.
regular coin image
Constans
I took the two images above with a flatbed scanner, and the image below,
showing a close-up of the mint mark, with a digital usb microscope at 40x enlarged.
Minted at the third officina (Γ) in Thessalonica (Saloniki, Greece) between September 337 and spring 340 A.D.

Reference:
Kent, J.P.C., "Roman Imperial Coinage", Volume 8 (RIC), Thessalonica, p407, nr. 57, obverse Cn2, reverse GE(b).
Carson, R.A.G., Hill, P.V., & Kent, J.P.C., "Late Roman Bronze Coinage" (LBRC),  Part I, p21, .nr 856.
Voetter, Otto, "Die Münzen der römischen Kaiser, Kaiserinnen und Caesaren von Diocletianus bis Romulus, Katalog der
hinterlassenen Sammlung und Aufzeichnung des Herrn Paul Gerin" (Voetter-Gerin), Antiochia, Constans, p45, #19.
Suarez, R., "Encyclopedia of Roman Imperial Coins II" (ERIC II),  p985, nr. 808 (B16, O8, R11, T39, M13, Exe: SMTΓ)
Suarez, R., "Encyclopedia of Roman Imperial Coins II" (ERIC II-eBook), Vol 4, p812, nr. 808 (B16, O8, R11, T39, M13, Exe: SMTΓ)
Sear, David R., "Roman Coins and their Values" (RCV Millennium Edition), Volume 5, p219, nr 18547.
Failmezger, V., "Roman Bronze Coins From Paganism To Christianity 294-364 A.D." (Failmezger), nr 381cCN.

General reference type (no detailed determination by mint mark or officina):
Van Meter, D., "Handbook of Roman Imperial Coins" (VM), p297, nr 51, variety with Ol/13.
Kampmann, U., "Die Münzen der römischen Kaiserzeit", 2e Auflage (Kampmann), p438, nr. 146.59.

Quality: Fine
Rarity:  C2