Open Culture has some post WWII posters and radio dramas which feature Superman combatting discrimination and the KKK. Membership in the Ku Klux Klan had begun to rise in 1946 and Stetson Kennedy, a human rights activist, comes up with an idea to combat their influence.

From the Open Culture website::

"The 16-episode [radio] series, “The Clan of the Fiery Cross,” aired in June, 1946 and effectively chipped away at the Klan’s mystique, gradually revealing their secret codewords and rituals."