In this article, I examine the name of a friend and correspondent of the fourth-century poet Rufius Festus Avienius, commonly identified hitherto as Flavianus Myrmeicus. After summarising the current state of research and translating the verse epistle which he received, I argue that, for a variety of reasons, Myrmeicus cannot be his name. Instead, it should be emended to Myrmecius, which was his signum: an example of a type of nickname which many Romans of elevated status in late antiquity bore in addition to their birth names. I examine Myrmecius as a signum within the context of late-Roman supernomina more generally, in the process clarifying how and in what circumstances and combinations they were used, and suggesting several sources from which they might be derived. I then explain how Myrmecius’ signum might have been mangled in the course of transmission, and conclude by noting that while the bulk of attested signa are found on inscriptions, Myrmecius suggests that many more may currently lie concealed in literary texts.