by Damyon Wiese.
I agree completion tracking is a better approach here.
(Although the 2.2 assignment only supported "Viewed" as a completion rule - you'll need at least 2.4 if you want to support "submitted" as a completion rule)
One issue with showing a different icon when the assignment is submitted is that it depends who is looking at the course - if student A looks and they have submitted, the icon will change and be cached and when student b looks he will see the cached icon even if he has not submitted.