Well actually there's no such thing as an irregular pentagon, it's either a pentagon or a regular pentagon... but that's not the point. Archer, my three year old son, held up this piece of Lego the other day and said, with glee, "Look Daddy, Superman!".
He was right. The vertically symmetrical pentagon shape was pretty much an exact match for Superman's insignia. The amazing thing is Archie has had practically no contact with the DC character outside of seeing the movie trailer a couple of times, playing with an action figure and sleeping under a duvet bearing his image.
Such is the power of iconography.
I once attended a talk at GDC presented by a somewhat aloof Toby Gard(of Lara Croft fame) which covered some other aspects of character design. One particularly interesting part of his lecture was to do with colour (I wish I could find his slides online, but they aren't in the GDC archives). He was able to show how Marvel and DC superheroes can be easily identified even if they are represented with simple blocks of colour. I've tried to recreate some from memory:
That's Batman and Spiderman. I'm not sure I've got it working quite as well he did, and he went on to show many more (Wolverine, Iron Man etc.) which all worked equally well.
I hear he's now back at Eidos after having some input on the recent Tomb Raider game. Do you Google yourself Toby? Could you send me those slides?