Alternate history narratives are virtually the same age as the concept of history itself, since musing about what-ifs, i.e., constructing counterfactual narratives have always been part of our effort to understand history. Although the theoretical implications about counterfactuality as a vehicle of conceptualizing history have long been subject to lively debates in the philosophy of history and the theory of historiography (e.g. see Evans 1999 & 2013, or Tetlock & Parker 2006), and the ontological and epistemological status of counterfactuals have earned scholarly attention recently (see Prendergast 2019), the semiotic aspects of counterfactual history as modelling activity have so far not been systematically studied. Neither scholarly accounts reviewing the narratological problems concerning historiographical narratives (see Doležel 2010, Fludernik 2010, and Jaeger 2015), nor analyses of counterfactuality from the perspective of fictionality and truth-valuation in fiction (see Pavel 1975, Lewis 1978, Doležel 1998, or Eco 2009) have paid any particular attention to the specific semantic problems raised by counterfactual histories and their consequences on the status of these narratives as semiotic models of historical processes. Examining statements of counterfactual history (and therefore also the possible worlds of these narratives) as sign-vehicles referring to their counterparts in the world perceived as reality by the audiences of alternate history narratives, makes it possible to explain their semiotic function of making sense of historical processes through modelling activity. Such an approach is especially vital in understanding the modelling process of counterfactual history narratives emerging in specific social media communities as acts of narrative co-creation.