You would naturally expect an inexpensive derailleur produced in Mexico in 1981 to be a copy of either a Shimano Skylark or a SunTour Honor. But this Mendoza model is possibly more of an, admittedly steel, copy of a 1970s Simplex Prestige. It has got two sprung pivots, like both a Simplex and a Shimano (but not a SunTour). But:
The outer parallelogram plate carries a rather fine image of one of the Mendoza company's signature products - the 1940s Mendoza RM2 light machine gun. Despite the close relationship between the firearms industry and the bicycle industry, I can only think of one other derailleur that was decorated with an image of a firearm - the BSA 4-Star.
This is one of two Mendoza derailleurs on this site, the other is here. They are very similar but have detail differences, for example in the pulley cage stop.