Greg picks up one of Tom's comics and Tom tells him it's Action Comics #23, in which Lex Luthor makes his first appearance. While Tom's statement is correct, when we see the comic book up close, it's titled "Atomic Comics", not "Action Comics".
Tom dresses up as Superman when he attends a comic book convention. However, his costume does not have the iconic "S" shield across the chest or on the cape. (This error may have been intentional to avoid trademark infringement.)