Nevertheless, variations on the term “Super Hero” or “Superhero” are jointly claimed by DC Comics and Marvel Comics as trademarks. Registrations of “Super Hero” marks have been maintained by DC and Marvel since the 1960s, including U.S. Trademark Serial Nos. 72243225 and 73222079.[66] In 2009, the term “Super Heroes” was registered as a typography-independent “descriptive” US trademark co-owned by DC and Marvel.[67] Both DC Comics and Marvel Comics have been assiduous in protecting their rights in the “Super Hero” trademarks in jurisdictions where the registrations are in force, including the United States, the United Kingdom, and Australia, and including in respect of various goods and services falling outside comic book publications.[68]

I did a search and found this article that goes into more detail. They applied for a joint ownership trademark to basically stop anyone else from using the term super hero in books, movies, games, toys and more, including shoes?! Pretty interesting.