On page 7 of Apple's Local and Push Notification Programming Guide there is a screenshot of the iPhone desktop, one of the application icons has a badge which does not contain a number - it is just plain red.
How is it possible to achieve this?
I think what you want to do is not possible with the current notification API. If you want to display the badge on your application icon, you must use the "badge" key in your APNS payload, and the value for this key must be an integer.
Even the local notification API has the same limitation, you can change the badge value with the applicationIconBadgeNumber property but, unfortunately, this property only accepts an integer.
It seems that only built-in apps (such as the phone app) can display a badge without number.
来源：https://stackoverflow.com/questions/10841605/how-to-give-an-app-icon-a-notification-badge-without-a-number