this might be a clue: For example, Thunderbird shows the unread message count, and Update Manager shows the number of updates available and a progress bar. The image shows these two examples: http://askubuntu.com/questions/197441/how-to-add-information-indicators-to-a-launcher-icon-from-a-script
This is a feature request for Unity QuickLaunch icon that shows the unread message count.
I believe it's a dupe of this bug... *** This bug has been marked as a duplicate of bug 2665 ***