"Also set along the façade are towers of superimposed variants of rain-god masks, topped by goggle-eyed masks representing the central Mexican rain god Tlaloc. The presence of Tlaloc masks has sometimes been interpreted as evidence of "non-Classic" cultural influences. Representations of Tlaloc occur frequently in Late Classic Maya art, however, appearing in contexts associated with warfare, bloodletting, and sacrifice. This may account for their prominence on the North Structure, where captives are publicly displayed. Because Tlaloc was the god of ancient Teotihuacán, these masks also lent prestige and legitimacy to Uxmal's rulers."
Kowalski, Guide to Uxmal, p. 50-51
My friend Marion Canavan writes, "Personally, I think the "Tlaloc" at the top is an anthropomorphic Venus symbol. In Mesoamerica the planet Venus always took the form of a male god. I was told by local guides at Uxmal that the two intertwined triangles, seen below the chin of the top mask, is a symbol for Venus. The same symbol appears on numerous stones on the site, some of which are labelled as Venus symbols in the Uxmal museum."