The Notification section allows users to select if they want to be emailed when a contact acts on an email such as opening an attachment, forwarding an email, changing their details, subscribing, unsubscribing or requesting a meeting. This section also allows users to select if they want to receive daily and/or weekly reports about email, campaign and contact activity.
The number in square brackets beside every notification 
indicates that there are notification records for that particular notification type. A new image indicates a new notification has arrived. 
Selecting the bulb or the On/Off link toggles the notification.