Help:Notifications/Popup documentation
Notifications Badge is a gadget that provides a "pop-up" badge on the top right of any WIkipedia page if you have any unread Notifications (as defined in your Notifications preferences). It was designed in response to concerns about the visibility of the new Notifications alert.
Though the gadget is ON by default for all registered users, you can easily turn it off by going to your Gadgets preferences and deselecting Notifications Badge under "Appearance", then saving.