Disable App Updates Available notification

[DrummerB]

An "App Updates Available" notification keeps popping up on my screen. How do I disable it? I disabled searching for updates automatically. There is no App Store entry in the Notification settings to remove, so I can't do that. I don't want to update, because I have an old version of Skitch and I don't want the dumbed down one that the Evernote team released.