The LL's in Superman's life..!
Since the very beginning of Superman's history, he has had several double L's appear in his life. It is not known if this was intentional or an accident at the beginning, but it seems to have turned into possibly an inside joke or a tradition.
This double L tradition even follows members of the Superman Family of books: Superboy, Supergirl and even the Legion of Super-Heroes have double L's around.
Now some are obvious, with the LL initials. But some take a little more imagination and creativity to find. But they are there if you look hard enough...