What is the blue hat with feathers called in Runescape?

Hello, I was playing Runescape last night on the Gnome agility course and saw a player there wearing a blue hat that looked sort of like a baret, but it had a couple white feathers coming out of it. My bf tried to ask him what it was called, but he wouldn't answer. Does anyone happen to know what this hat is call?

It's from the mobilizing armies minigame ( untradable ). I think it's the sargent level cap.

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