Watch List notes:

Constantine I. A.D. 307/10-337. AE half follis (17.33 mm, 1.75 g, 7 h). Rome mint, struck A.D. 312/13. FL VAL CONSTANTINVS AVG, laureate and cuirassed bust of Constantine I right / PACI P-ERPET, Pax standing facing, head left, holding olive-branch and standard; in field, XII // RT. RIC VI 356. 

The meaning of the numeral XII in the reverse field is not known