importance indication; priority display
Computing term for a visual or system-level indicator showing the importance or priority of an item, such as a flag, color, or label.
In this software, you can attach an importance indication to emails.
優先度 refers to the abstract concept of priority level, while 重要度表示 is the concrete display or indication of importance.
Compound of 重要度 (importance level) + 表示 (display, indication).