A trademark's enforceability hinges on whether the public is likely to associate a word or mark with a given company -- in other words, when you hear the word "super-hero," if you think "Marvel and DC," then Marvel will be able to go on censoring and eliminating its competition.
One way of accomplishing this dirty bit of mind-control is by adding a ™ symbol after the word "Super-Hero." That TM lets the world know that you claim ownership over the word it accompanies. If you can get other people to do it, too, eventually you may in fact get the world to believe that the word is your property -- and then, it becomes your property.
"Super-hero" isn't Marvel's property. They didn't invent the term. They aren't the only users of the term. It's a public-domain word that belongs to all of us. Adding a ™ to super-hero is a naked bid to steal "super-hero" from us and claim it for their own.
The latest trick in its move to steal the word is using the ™ symbol in the bumpf for its California science centre show -- they've recruited a science museum to help them steal "super-hero."
Here's a proposal: from now on, let's never use the term "super-hero" to describe a Marvel character. Let's call them "underwear perverts" -- as Warren Ellis is wont to -- or vigilantes, or mutants. Let's reserve the term "super-hero" exclusively to describe the heros of comics published by companies that aren't crooked word-thieves.