Marvel & DC's Super-Hero "Claim"
Marvel and DC have been claiming and attempting to enforce this "trademark" for many years. According to this link (one of several) from the US Patent and Trademark Office's "Trademark Application and Registration Retrieval system," Marvel & DC claim a "First Use in Commerce Date" of October 1966. Most knowledgeable folks aggree that this claim is bogus on many levels, but that hasn't stopped the USPTO from allowing the publishers to register the claim successfully and repeatedly over the past few decades. Digging around the archives via TESS reveals that all TM claims aren't automatically registered - some are denied. But from what I can tell, they've never denied Marvel & DC's claim.
Apparently, just because the USPTO allows you to register a trademark doesn't actually mean that they're endorsing your claim's validity - they're just aggreeing that, well, you've made the claim (tax dollars at "work," folks!). I suppose if someone with deep enough pockets and stamina to spare were to take Marvel & DC to court over this, the claim's bogus nature would be revealed and overcome. But until then, these two "super-gorillas" continue to throw their imagined weight around.
Thanks to several folks at the Comics Scholars Discussion List for helping me figure out what I think is going on in this situation. Caveat lector: I ain't no lawyer!