Interesting thin metal gilded pin in the shape of a boomerang and embossed with:
Boomerang is about 55mm wide with an attached suspension. This one has a tri-colour ribbon through the suspension and a brass safety pin attached to the ribbon.
Badge probably dates to March 1918 when the “Our Boys” carnival was held around Victoria to raise funds the war effort. This article on Trove refers to the inadequate boomerang souvenirs or pins.