This is a good tip.
Maki from Justbento.com, one of my favourite factual bento sites has gleaned this tip from a Jap Magazine.
"... there was a tip to put crisscross lines on top of the rice packed into a bento box, to not only make the rice look a bit prettier, but to make it easier to pick up with chopsticks." More
Nice!! I shall try this next!