This is a discussion on On my ipad 2 the app icon has a number 1 on it, how do I get rid of it? within the iPad FAQ forums, part of the Apple iPad Discussions category; Don...
If you mean the App Store icon, it indicates that one of your apps has un update available.
It will stay there until you actually update that app. I have 11 showing right now, because I like those apps how they are at the moment.
Cool, have fun!