A hair clip
A hair clip was an accessory an individual could place in their hair to keep it together.
Lieutenant Jadzia Dax usually wore a hair clip. (DS9: "Emissary" et al.)
In 2372, she traded her hair clip for passage to the hospital on the Teplan homeworld in the Gamma Quadrant. (DS9: "The Quickening")
The Species 8472 replicant impersonating Valerie Archer wore a hair clip. (VOY: "In the Flesh")