Here is a coin that is not in RIC that just sold for US $461.01. It is unlisted for the field marks S/F; though RIC does list SE/F.
Drost lists three for Maxentius and also examples for Maximianus and Constantine as Caesar.
Maxentius
A.D. 307
28mm 10.4gm
IMP MAXENTIVS P F AVG; Laureate head right.
CONSERVATOR AFRICAE SVAE; Africa standing left, holding labarum and tusk; at feet, lion with captured bull; S-F across fields.
In ex. B
RIC VI Carthage --; Drost 23
