Your coin does not have a star in the mintmark, but a dot in the exergue. The author of RIC, Patrick Bruun, mentions this coin in the footnotes....
It Rome mint-- SM leaf RB
I've got an example of the earliest Licinius campgate with SMHT mintmark [ATTACH]
I also agree that it is unofficial. I have had some good style unofficial coins copying Ticinum, like the two below. [ATTACH] [ATTACH]
This is RIC VII Cyzicus 55 with annulets on the diadem. [ATTACH]
These orbs are usually believed to be celestial spheres rather than the earth...of course there is always debate. see 'Symbolism of the Sphere'...
[ATTACH] Constantius I A.D. 294-5 Ӕ Antoninianus 23x24mm 3.3gm CONSTANTIVS NOB C; Radiate, draped and cuirassed bust right. COMES AVGG; Minerva...
the Constantine is 22mm and the Gallienus is 21mm
because the countermark assigns it a value.
from my Carthage page (which I linked to earlier) Some of the references below have two RIC numbers. That is because RIC breaks up this issue by...
I also have a Gallienus with the same countermark [ATTACH]
[ATTACH] Constantine I struck A.D. 312- 313 and countermarked as a Spanish 4 maravedis, circa 14-15th century.
I have a page on these Carthage issues-- http://www.constantinethegreatcoins.com/Carthage/
nvm
You can get these IOVI coins for all the members of the Tetrarchy, though I do not have a Galerius. [ATTACH] Maximianus A.D. 293- 294 20x22mm...
PXV in the exergue is the Tribuncian year for Gallienus (A.D. 267)
here's a smaller AE2 from his brother Valens. [ATTACH] Valens A.D. 364- 378 Ӕ2 22mm 4.4g D N VALEN-S P F AVG; pearl-diademed, draped and...
this one is from the Mildenhall Hoard of 1833 [ATTACH] Salonina A.D. 256- 257 Ӕ Antoninianus 19x25mm 3.4g SALONINA AVG; Draped bust right,...
[ATTACH] Diocletian A.D. 292- 293 Ӕ Antoninianus 22x23mm 3.1gm IMP DIOCLETIANVS P AVG; Radiate, draped and cuirassed bust right. IOVI AVGG;...
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