The purpose of the Notifier is to provide a visual cue to the user that depends on the value that a field contains.
You basically assign a different image to different conditions and the control displays the corresponding image when the condition is met.
In the example below the notifier is tied to an expiration date. Depending on today's date (in this case it was Nov. 24, 2004), it displays a different icon to indicate that the expiration date is still more than 5 days ahead, less than 5 days ahead or passed.
You may also use the notifier to visually identify your records based on the ID/Status value for example.
See this video on how to set it up.
Additional information found at BestACTAddons.com