In A.D. 316, Constantine and Licinius began a civil war. Tensions must have been building for some time to finally reach the point of war. It might seem unusual though, that there is not much of a record of this in the bronze coinage. The clearest indication of hostilities in the coinage is actually the lack of coins- each ruler stopped minting coins in the name of his rival. This conspicuous absence indicates that something is definitely wrong.
If you look closely though, you can find some hints that there is something wrong. For example, the mint of Rome issued some coins that tell a subtle story of the break between the two Emperors. There were a few SOL INVICTO issues from the period of 315- 316 that are different from the normal type. The first looks like a regular Sol type except for the reverse legend of SOLI INVICTO COMITI D N (see RIC VII Rome 46 below). The second Sol type has changed a bit, Sol now holds a victory on a globe and the reverse legend is SOLI INVICT COM D N (see RIC VII Rome 49 below). With the small addition of D N to the reverse legend, these coins now tell a much bigger story. D N is the abbreviation of domino nostrorum (our Lord), so these coins seem to be stating that Sol is the companion of only Constantine, not Licinius. The third Sol type (see RIC VII Rome 52 below) has a captive to the left of Sol. In 316- 317, Rome only issued these three coins in the name of Constantine and the meaning of the captive seems pretty clear, it symbolizes Licinius.
