The contest's rules permitted me to submit two entries. My first, that wasn't selected, is the following:
The blue stripe represents the river Cam and, together with the red stripe placed like a bridge, is a pun on Cambridge name. The three Saxon crowns on red is took from the coat of arms of the Diocese of Ely, and the three crowns on blue are the coat of arms of East Anglia. The yellow background represents the county's fenlands, and keep the recommendation of using a maximum of three colors.
My second design, that I made in a fast but determined way, is a derivative of the first, but with a better realization. That was selected as a finalist:
The symbolism of the former was kept, but with many improvements: the crowns are now three, in a more direct counting; the river gained some life, with the waves, and was colored in a shade near "Cambridge blue", the color of the traditional University of Cambridge. It represents county's landscape, history and prides in a very ellegant way.
Comments are welcome.
You can vote in your favorite design in the end of this page.