Depicts the seal of the United Mexican States.

The Seal of the United Mexican States is a modified version of the national coat of arms, with the addition of the full official name of the country Estados Unidos Mexicanos, in a semi-circular accommodation in the upper part of the seal. Current and past Mexican peso coinage have had the seal engraved on the obverse of all denominations.

The coat of arms depicts a Mexican golden eagle perched on a prickly pear cactus devouring a rattlesnake. To the people of Tenochtitlan this would have strong religious connotations, but to the Europeans, it would come to symbolize the triumph of good over evil (with the snake sometimes representative of the serpent in the Garden of Eden).

On a 12-sided field, at center, the denomination 20¢ with the date above and the mint mark Ṁ below. From upper left to lower right, a partial border of the stylized designs from Reed (Acatl), the 13th day on the Aztec calendar stone (Piedra del Sol).

The Sun Stone, Stone of the Five Eras, or sometimes (erroneously) called Aztec calendar stone is a late post-classic Mexica sculpture housed in the National Anthropology Museum in Mexico City, and is perhaps the most famous work of Aztec sculpture. The stone is 358 centimetres (11.75 ft) in diameter and 98 centimetres (3.22 ft) thick, and it weighs about 24 tons. Shortly after the Spanish conquest, the monolithic sculpture was buried in the Zócalo, or main square of Mexico City. It was rediscovered on December 17, 1790 during repairs on the Mexico City Cathedral. Following its rediscovery, the calendar stone was mounted on an exterior wall of the Cathedral, where it remained until 1885. Most scholars think that the stone was carved some time between 1502 and 1521, though some believe that it is several decades older than that.