I just did this video on how and I thought I might as well put it up here.
[ame=http://www.youtube.com/watch?v=GlXnPa45478]YouTube - How to add your own icons to OpenNotifier by TheRealTylerRau[/ame]

Don't Know about OpenNotifier? Briefly its an open source application for iOS that lets you add your own icons to the status bar when an application has a badge notification on it. It also allows you to as Pseudo-Badges for apps that don't come with Badge capability.