The notification icon shows a stylized bowl upside down when the bell is muted. Otherwise the notification icon shows a stylized bowl opened to the top. MindBell switches the notification icon when muting/demuting, that is meant by the bell is turned over.

Due to a bug (in Android) MindBell doesn’t get informed in time about muting/demuting when enabling/disabling the new do-not-disturb modes (introduced in Lollipop and Marshmallow) by switching from tab to tab between total-silence, alarms-only and priority-only - along the arrows in these screenshots:

The only “solution” is a bypass with three ways to update the notification status which turns over the bell correctly: (1) Manually use status refresh button in notification. (2) Manually open and close settings. (3) Automatically when the bell rings.