The Notifier is a small utility that lives in your system’s tray or menu bar. It continually signals you the status of the Portmaster Core Service via colored status indicators in the icon. If you have Desktop Notifications enabled, the notifier takes care of relaying them to your operating system.
You do not have to open the full Portmaster UI for more details or to make changes: If something goes wrong, you can get a first impression of what is going on by clicking the icon to open the menu. There you can quickly react to changed circumstances and switch your network rating.
Extended documentation of the Notifier are yet to be written. You can check out its source code in the mean time.