I assume you're familiar with Superman.
Kal-el. The man of steel. Last son of Krypton. The man of tomorrow. Tall guy, dark--
Anyway, it's a safe bet that you're familiar with him because most of the world is to some degree or another. He's a role model and an icon, more recognizable than presidents, popes and kings. Some of it has to do with the red cape and blue suit. Some of it is that big, red shield spread across his chest. Over the last seventy-five years, it has become a symbol that is as widely recognized as its wearer. The stylized shield is tied to his name.
Since his arrival, we've known him by it. That's what a symbol is for: a shorthand reference to quickly evoke all it has come to embody. In Superman's earliest lore, nothing was said of it. It was just a part of his clothes. Later, when his Smallville background was explored, its creation was attributed to his adoptive father, Jonathan Kent. That element of his story held sway for several years. Superman: The Movie, however, put forth the idea that it was not only his symbol on Earth, but that of his family, the house of El, on Krypton. That planted seed gradually flourished, replacing previous notions to the point that the symbol became a part of the Kryptonian alphabet.
Now, it's not even a stylized "S". It seems pretty silly for Superman to contend that it isn't one without even acknowledging that it resembles an "S". He may not be from around here, but he's not new here either. It may no longer mean "Superman" literally, though it is no less his symbol, but it has certainly never stood for "Stupid". Granted, there are those who might argue even that point with as many times as his scribes have had him unwittingly blunder into the clumsy kryptonite traps of an underachieving Lex Luthor or just charge into the radioactive substance's area of effect by failing to use the multitude of heightened senses and superpowers with which he's long been graced.
Pardon my penchant for tangents, but Eve Tessmacher did have a great point when she told her boss that he wouldn't be able to get within a mile of the big blue boy scout with a glowing green rock. Even tricking him into opening the lead box himself should've only resulted in his closing it faster than most of us would recoil from a hot pot on a stove. Beyond even the consideration of super-fast reflexes kicking into gear at the first hint of such potently debilitating radiation, he's not super-arrogant or uber-overconfident. When he's charging into the lair of a resourceful king of supervillainy (his PR people insist on such adjectives) who seems undisturbed by the visit, you'd think Superman would exercise sense enough to check for traps, killer robots, mad scientist superweapons of mass destruction... They haven't let Lex Luthor or really anyone but Zod flex the hardcore superscience muscles on-screen yet, but the real Luthor (the one who's a serious threat to Superman) could run workshop's for James Bond's villains. Maybe he does. That would explain where they get their toys, which is about what Luthor would consider them to be. Or maybe science projects. Most of his evil genius steers toward better and better ways to assault Superman. That means producing higher order output and plans than "Guess which hand I have the kryptonite in." Great heroes and superior villains make each other bring their best game to the playing field. If you're going to put all that into a movie or on TV, we want to see it.
Now, as I was saying, the symbol endures. There've been mystifying alterations to Superman's clothes and background, but the symbol endures. Still, it's no longer an "S". Sure, it still looks like an "S", but now it's both part of the Kryptonian alphabet and the Kryptonian symbol meaning "hope". In Man of Steel, when he refuses to acknowledge to Lois that the swirl on his chest looks like an "S" (even though he has lived on Earth as long as he can remember), I have to take her side. Contemporary writers have chosen to pack both personal and public meaning into Superman's symbol, making it his family's crest and the representation of "hope". Don't get me wrong, I've always got Superman's back, but the Lois POV makes more sense to me this time: whatever you want to call your swirly chest shield, it looks like an "S" so come up with a name to go with that...something that sounds catchier than "Hopeman". Being hopeful may sound positive, but it doesn't carry the impetus of definitive confidence that "super" does.
Let's face it, you fly around doing what Superman does and you're going to inspire most people to feel something about it. The ones who have time to ask "What's the 'S' stand for?" and those who later hear the explanation of the chest swirl are going to be a lot more responsive to the short answer "Superman" than they will be to getting a lecture about having a flag of hope waved in their face. Using your superhuman powers to help people is wonderful and selfless. It's the sort of thing that's generally well-received. Telling people how to feel about it is pushy and I don't think anybody likes that.