This coin is not listed in RIC for this mintmark. It is listed in Lech pagè and in Cloke-Toone.
It should come after RIC 4.
Constantine I, 313 circa,
IMP CONSTANTINVS AVG, bust r., laur., cuir.
PRINCIPI IVVENTVTIS, Emperor in military dress, stg. r., holding transverse spear and globe, cloak spread. S in left field, F in right field. PLN in exergue.
20mm, 3 gr.