The curator at the Golden Age blog is a tireless servant to our compulsive appetite for garish stereotypes. The latest entry, jump here, with tawdry Spicy Western Stories samples, has almost every flavor of ethnic criminality and swarthy viciousness that one might imagine--see sample above. 1937 was a particularly good year for scary "Mexican" covers with two, by H. J. Ward, that belong in the Tex[t]-Mex Stereotypes Hall of Fame.
Here are a couple more, from the Spicy-Adventure Stories line: