In August 2019, a large-scale series of fires struck the Amazon rainforest in Brazil and neighboring countries. The event generated great national, transnational (other Amazon region countries), and international commotion. The collective actions were visible in media environments such as WhatsApp, online social networks, and the press. The dispute of meanings was driven by media positioning from various and conflicting local identities, such as indigenous tribes, rural producers, prospectors, loggers, and environmentalists, as well as celebrities and representatives of international governments. Several hashtags permeated the collective actions in this scenario, including the hashtag #PrayforAmazonia, which reached online trending topics worldwide and mobilized international public opinion. The semantic ecosystem of hashtags in this context, including the ubiquitous #PrayforAmazonia, circumscribed political positions in media formats. In this chapter, we aim to understand how the dominant trajectories of hashtags related to the Amazon fires reveal the transmediatic dispute of meanings among different identities. The theoretical framework revolves around concepts such as transmedia identity transmedia mobilization and hashtag activism, and builds on the work done in these areas by previous authors. The methodological approach is twofold. First, there are the data mining procedures with automatic collection on Twitter and in public WhatsApp groups between August 11, 2019, the starting date of the fires, and September 11, 2019, a month later. The corpus is constituted by the trajectory of events connected to the fires, which are associated with hashtags in the national, transnational, and international Twitter trending topics, and related to the most shared themes and images in Brazil in the public WhatsApp groups. Second, there is the analytical phase in which the dispute of meanings is analyzed based on Peircean semiotics, considering the hashtag as a mediator sign of varying positions related to the interpretants generated and the collateral experiences that accompany them. The findings point into the direction that the communicational process permeated by hashtags has a transmediatic nature, singularized by the variety of interpretants generated in tune with the multiple identities that cross the event investigated.