I just won this one from the latest ROMA auction. It is special because of the cryptogram in the mintmark but it is also supposed to be from a hoard, as the collector ticket says "ex C. B. Hoard" though I don't know what hoard that is, if it is even published. Fortunately, it came from a British collectors collection, so I might be able to find some info in one of the Coin Hoards from Britain books.
Constantine I BI Nummus. Rome, AD 320. CONSTANTINVS AVG, helmeted and cuirassed bust right / ROMAE AETERNAE, Roma seated right on round shield, holding another round shield inscribed X-V in two lines; RЄѠCP (ЄѠ ligate) in exergue. RIC 194 corr. (Roma seated left). 3.63g, 19mm, 6h.