I wrote a little python program that does what you're looking for. It's a bit rough around the edges, so I'd appreciate any feedback you might have.

ubuntu git indicator

To use it, run git-indicator from a directory that contains one or more git repositories (like you'd use git-dude).

Example:

~$ git clone https://github.com/itsadok/git-indicator.git ~/.git-indicator

~$ cd ~/repos

~/repos$ ls

repo1 repo2 repo3

~/repos$ ~/.git-indicator/git-indicator.py &