According to native Mexican legend, the Aztecs were told by the gods to settle and build a city where they saw an eagle in a cactus by a lake. The modern version of this legend includes that the eagle would have a snake in its talons. However, scholars of ancient Mexican history find no mention of the snake in the earliest references to this legend.
Regardless, this is given as the reason for the location the Aztecs chose to build the center of their civilization, the city of Tinochtitlan. This is the site of the present-day Mexico City.
The Taco Trio logo features an eagle with a snake around the border in recognition of this founding legend.