xiuhcoatl.

"According to the myth of the birth of Huitzilopochtli, the Aztec patron god used the xiuhcoatl (plural, xiuhcocoah), which means 'fire serpent,' as a weapon to decapitate his sister Coyolxauhqui. The xiuhcoatl consequetly became a national and political emblem.
Manuel Aguilar-Moreno, Handbook to Life in the Aztec World (2007), 195.

Two Reed appears on the bottom of a stone carving of Xiuhcoatl (held at Dumbarton Oaks), along with the glyph for Moteuczoma. This year marker referred to the New Fire Ceremony of 1507.
Patrick Thomas Jajovsky, On the Lips of Others: Moteuczoma's Fame in Aztec Monuments and Rituals (Austin: University of Texas Press, 2015), 88, 91, fig. 5.5.

xiuhtecuhtli = the serpent fire device, the symbol of fire drills
Justyna Olko, Turquoise Diadems and Staffs of Office: Elite Costume and Insignia of Power in Aztec and Early Colonial Mexico (Warsaw: Polish Society for Latin American Studies and Centre for Studies on the Classical Tradition, University of Warsaw, 2005), 128.