Copyright 1964 by National Periodical Publications, Inc.
This story is a (rare) sequel to "The Sweetheart Superman Forgot!" from Superman (DC, 1939 series) #165.
Also known as "The Great DC Contest!" The contest of this story is that the letters D and C only appeared once, at the bottom of page 3 as "CONTINUED ON NEXT PAGE FOLLOWING". But the irony is in the Superman in the Sixties reprint, DC eliminated that caption, while still challenging the reader to find the hidden letters!
However, although letters D and C were not intended to appear, one Bizarro says the word "Goodbye", whilst another says "and", on page 2, panel 5.