Constantine I as Caesar (306-307 A.D.) -  AE Follis - 27mm, 9.18g
Obverse - FL VAL CONSTANTINVS NOB CAES
Constantine I, his laureate head right.
Reverse - GENIO POPV-LI ROMANI                              
Genius standing left, modius on head, naked but for
chlamys over left shoulder, holding patera (from which
liquor flows) in right and cornucopiae in left hand.
E in right field, ANT : in Exergue.

The image below was photographed by Sand and Swamp Antiquities. The image above is my own scan.
Minted at officina E in Antioch (Antakya, Turkey) between July 306 and early spring 307 A.D.

Reference:
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), 1921, Constantine Magnus, #1
(specimen in the collection of Paul Gerin, from officina A, Γ and S)
-Kent, J.P.C., "The Pattern of Bronze Coinage under Constantine I", Numismatic Chronicle, 1957, p 69, #1086
-Sutherland, C.H.V., "The Roman Imperial Coinage" Volume VI, 1967, p624, note 5: "This issue, save for Constantius,
continued without change at the beginning of Group III, except that no coins of Severus as Augustus (though included
by Kent, N.C. 1957, p. 69, no. 1084) are known to me".
-Sutherland, C.H.V., "The Roman Imperial Coinage" Volume VI, 1967, p627, Note: "As indicated above, p. 624, n. 5,
the aes of Group II (ii) continued into Group III with unchanged Genio Populi Romani folles for Galerius and Maximinus
(though probably not for Severus as Augustus)....".
-Bastien, Pierre, "Trouvaille de folles au Liban (294-307)", Revue Numismatique, 1967, Aleppo & Homs, Syria Hoards, table p171.
-Bastien, Pierre, "Trouvaille de folles au Liban (294-307)", Revue Numismatique, 1967, Lebanon Hoard, p188, #76.
-King, C.E. & Spaer, A., "A Hoard of Folles from Northern Sinai", Numismatic Chronicle, 1977, p106, #4000-4009.
-Salzmann, D., "Folles of Severus II as Augustus and of Constantine I as Caesar from Antioch ", Numismatic Chronicle, 1983,
p214-216 and plate 42, #7.

See my page on Constantine I as Augustus - The "lost" Genio Populi Romani issue from Antioch
This coin is listed at Not in RIC.

Quality: Fine+.
Rarity: Unclear, but probably Scarce (not rare).
So far I have been able to confirm the existence of at least 8 specimens of this coin from
officina E, so according to the definition of RIC Vol VI, that would make it's rarity R3 (but there are probably more out there).
I also own another specimen from this officina which you can find here.