if you own a trackball (which the entire computer industry of geeks SHOULD use) you would guess that its a pic of the trackball. the green part is curvy like the shape, the circle is the ball, and those lines are the bottons. notice 1 of them is red, just like the scroller on the trackball.
everytime I see it, it reminds me of the trackball, but logitech maybe wanted it to look all abstract and unique so they tweaked it a bit.
my $1.00 on it
danny~!