Actually that was the official title of the 1996 Warner Bros. animated series that's more commonly known as Superman: The Animated Series.
I think you have that reversed. The title of the 1996 cartoon was always Superman: The Animated Series
, but was often times simply shortened to Superman
for promos and TV listings.
Interestingly, the show never showed its title during its run.
As an interesting aside, the show was then later retitled The New Superman Adventures
when it combined with The New Batman Adventures.
(since Donner's movie was called Superman: The Movie, however I am not sure if it was credited during the opening title sequence as just Superman or not).
The title as displayed in the film was simply Superman