New Items Indicator on Button

[TheIgster]

It's quite easy of course to import an image and make it a button, allowing the user to use a customized button to open 'Messages' for example. My issue currently is being able to add a new items indicator image to that button. I've seen themes that do this and I'm not really sure how they did.

So for example, I import a big button image that says Messages on it. I convert it to a button in Composer and set the actions for the button to launch the messages application. Does anyone know how I can get this button to also display a new items indicator? If there some flag I can set or some action I can use to set the state of the button to needing to indicate there are new items for it?

Thanks to anyone who can help with this.