First mention of Daily Planet in comic book.
This is the first story with Luthor. Superman asks "Who is Luthor?" The second Luthor story appeared in Superman #4 (cover date Spring 1940). Luthor says "We encounter each other once more".
However Superman #4 may have gone on sale before this issue. In their copyright registration, Detective Comics, Inc. said Action Comics #23 was published Feb 23, 1940. An in-house ad said Superman #4 would go on sale Feb 15; the copyright registration said that it was published Jan 23. Officially, per DC Comics web site, Luthor's first appearance is in Action Comics #23.
Luthor has red hair.
The last panel of this story is an illustrated promotional ad for the Sandman in Adventure Comics.
Title is given in panel 3, page 1 of story.
Writer credit added and art verification by Craig Delich.
Letterer credit added by Craig Delich.
Page includes many small ads from stamps dealers.