When challenged to draw Superman, a very fun way to portray him is in silhouette.
Not that he's hard to draw--he's terribly easy, in fact--it's just that in Frank Miller's
BATMAN: THE DARK KNIGHT RETURNS this was how we often saw him. But then again, maybe it was only once or twice and the image is just so strong that it stuck? Like an image
will, when it flashes in stark relief in front of your eyes.
Either way, it adds an heir of mystery and darkness...
a kind of otherness to him--being the god-like alien that he is.
And that may help us realize further that that's how Miller's gritty old
Bats saw Superman, golden boy behind the red, white and blue.
Regardless, he looks cool that way.