The 50 Pesos coin is called "Centenary" because it serves to commemorate 100 years since the promulgation of the Mexican Declaration of Independence (in the original, Acta de Independencia del Imperio Mexicano) on September 28, 1821.
The reverse of the coin symbolizes the Winged Victory, represented in the monument of the Angel of Independence (located on Paseo de la Reforma in downtown Mexico City), together with a background of the legendary volcanoes Iztaccíhuatl and Popocatépetl.
"50 PESOS 1821 1947 37.5Gr. ORO PURO"
"50 Pesos 1821 1947 37.5Gr. Fine Gold"
"ESTADOS UNIDOS MEXICANOS"
"United Mexican States"
On the edge:
"INDEPENDENCIA Y LIBERTAD"
"Independence and Liberty"
The picture is just an example. We could also have available coins with other dates.