Wikipedia
In the Aztec culture, Tecpatl was a flint or obsidian knife with a lanceolate figure and double-edged blade, with elongated ends. Both ends could be rounded or pointed, but other designs were made with a blade attached to a handle. It can be represented with the top half red, reminiscent of the color of blood, in representations of human sacrifice and the rest white, indicating the color of the flint blade.
It was the sign of the eighteenth day, the twentieth day of the month of the Aztec calendar and the beginning of one of the twenty trecenas of the tonalpohualli.
The Tecpatl knife was traditionally used for human sacrifice by the Aztecs, but it also was the short-range weapon of the jaguar warriors. Although it may have seen only limited use on the battlefield, its sharp edges would have made it an effective sidearm.