The bonnets real meaning was to protect the wearer. The feathers on the bonnet had to be earned. And a bonnet could never be worn with out consent of the chief.
The feathers mean that the warrior was at the very front of the fight. Feathers were notched to tell of the event of the story. Such as killing, capturing an enemy's weapon and shield and if the Warrior was of foot or horse back. A Chiefs feathers was earned from doing good deeds for his tribe.