Once updated, the notification will display a page letting you know of the update. The bullet points on this say:
When you visit a site connected to a Google+ page, a slider will appear on the side of the browser window. Hover over the slider to expand it and easily add the page to your circles.
The notifications button in your browser will be badged with a "+" to indicate when you're viewing a site connected with a Google+ page. Clicking on the button shows your notifications just like it did before but now it will also display the related Google+ page information and provide a quick way to start following it.