User Configuration > Administrative Templates > Microsoft Project 2016 > Project Options > Interface > Show indicators and Option butons for
User
HKCU\software\policies\microsoft\office\16.0\ms project\options\interface
Specifies that the feedback triangle should appear in a corner of a field if the user assigns additional resources to a task that already has resources assigned. If you enable this setting, a feedback triangle is displayed in the corner of a field if users assign additional resources to a task that already has resources assigned. If you disable or do not configure this setting, the user's default setting is used.