On many of the VLPP's with this bust it looks like Constantine is holding something in his left hand. I am convinced now that he is sometimes holding a mappa, like the earlier billon coinage from Trier. It is not always clear though, and I suspect, like some of the billon coinage (see last image) there is no left arm or mappa. So actually two bust types- one with right holding spear and left holding mappa and the second with spear over right, but no left visible-- either it's not present or off the flan or otherwise not discernible due to strike, wear or corrosion.
Constantine I
A.D. 319
17mm 2.9gm
IMP CONSTAN-TINVS AVG; high crested helmet, cuirassed, spear over right shoulder.
VICTORIAE LAETAE PRINC PERP; two Victories stg., facing one another, together holding shield inscribed VOT P R on altar.
in ex. TARL
RIC VII Arles 195