After the murder of Caesar, there was a lot of maneuvering around the vacuum of power left behind. Antonius had been Caesar's right-hand-man and he, along with Lepidus, were immediate candidates to become the new VIP in the faltering Roman Republic. Antonius was known to Caesar's large, experienced, and very dangerous legions, but suddenly there was a newcomer on the scene: Octavian, Iulius Caesar's grand-nephew, calling himself "Caesar" and openly attempting to gain favor with the legions by using his famous (and assumed) name. Octavian was young, inexperienced, but he had Caesar's money and he was liberal in doling it out as bribes and promises to the legions. Late in 44 BCE it was a no-holds-barred contest between Antonius and Caesar Octavian for influence with the armed element of Roman society. Meanwhile, back at Rome, the remnants of Rome's political machine were similarly doing battle (with words) in the Senate as to which, if either, of the two would be given their support.

Skipping ahead: by the end of April of 43, the next year, Antonius had "lost" the political battle at Rome and had been branded a hostis: a public enemy of Rome. Lepidus, who had been powerful from the start of the business, was quietly biding his time in Gaul with the balance of Caesar's veteran legions. Antony, who had been fighting in northern Italy for months, slipped across the Alps and arrived to Lepidus. Instead of negotiating, he just took control of the legions without a fight and Lepidus could do nothing. See here for more on that.

Your coin was struck (edit: in Gaul, by Antony) at the end of May 43 BCE, when Antonius assumed control of the legions in Gaul. Like most ancient coins, it was loaded with propaganda: for the legions, it announced that Antonius, Caesar's "master of the horse" and a long-time soldier, was the natural successor of Caesar and therefore most worthy of their support. He did not have Caesar's name, but he was imperator. The suggestion is that Octavian was just a kid with a famous name, without experience, accolades, or real connection to the dead dictator. That same coin, when it circulated its way down into Italia, proclaimed that Antonius, now that had installed himself in Gaul, was the actual and conceptual successor of Caesar. There are more sinister overtones, as well: not long before, those legions had followed their imperator as he invaded Italia and Rome in the face of an uncooperative senate. This coin must have reminded the senate of that invasion of 49 BCE and called to mind the spectre of another conflict with those very dangerous and very experienced armies.

Octavian was formally "adopted" by Caesar and installed as consul in August, and it seemed that all the pieces were in place for another disastrous civil war. Rome had been in almost constant civil conflict for decades, and everyone was weary. How fortunate, then that not long after Octavian, now secure in his position as a contender for supreme power in the Roman state, went to visit Antonius and his dangerous legions in Gaul and managed to come to an agreement. The two of them (and, oh yeah: Lepidus too) would be the IIIviri rei publicae constituendae: the triumvirs responsible for restoring the Republic. The second triumvirate was born, which married Caesar's (now-)legitimate heir with the military experience and authority of Antonius and Lepidus. It wouldn't last, of course, but in November of 43 it must have seemed like the whole world had taken a step back from walking over yet another cliff.

Cicero's correspondence in letters is one of the best, but also most complicated sources for this period. He was in constant contact with some of the major players, including Octavian, and we have preserved a huge archive of Cicero's letters. Unfortunately, they are very difficult to read for anyone who is not steeped in the ins and outs of Roman politics. Lots of names, lots of oblique references. The easiest way to read about this very complicated period as a narrative is the chapter by Rawson in Cambridge Ancient History IX. Unfortunately, that is hard to get and very expensive. I'm actually having a hard time finding an accessible, readable source that lays out the narrative of 44-43 BCE--maybe another contributor can help out here. These two years are in the middle of two major epochs and seem often to fall through the cracks between the "Late Republic" (which they want to end at the murder of Caesar) and the "Augustan Period" (which they want to begin with the second triumvirate, at the end of 43, or else after Actium).