There's no built-in way to draw a badge. The only built-in badge support that I know of is to add a badge to your app's icon on the springboard (maybe something also for tabs in a tab controller). There's a certain amount of source code floating around to do that so look for it.
It would be pretty easy to create a custom subclass of UIButton that has the option to display a badge. Then the view controller that manages the button could set the button's badge value as needed.