In Superman #19 (September 1942), we find what I can only assume is an intentionally-whimsical story in which Clark Kent takes Lois Lane to the movies and Clark has to prevent Lois from seeing key parts of the Superman cartoon to protect his actual secret identity from being discovered. Of course this makes no sense from the in-universe logic that has been set up thus far (why is it ok for every other person to learn of Superman’s secret identity but Lois Lane?!?), but I suppose it was amusing to read at the time, given how popular the cartoons were reported to be.
The story also establishes the odd fact that Siegel and Shuster live on the same Earth as Superman and know all his secrets…