http://en.wikipedia.org/wiki/Heraldry Heraldry. It was originally designed to let people work out just who the hell was actually in all those metal suits with faceless masks. Its embarrassing when you accidentall attack and kill your own king after all... Hence the rules are actually pretty simple. Take the shields and split them into a few (2 or 3 max) different zones with different colours. There are some rules about putting "colours" and "metals" next to each other, but they are entirely designed to help with visual acuity at a distance.
Shapes should be simple and bold. If you're doing a squad you could maybe choose simimlar shapes deon in different colours, or alternatively keep the same colours and modify the shapes or motifs.