The bearhead is obtained upon defeating The Kendal during the Mountain Daughterquest. Along with the Corpse of woman, it is proof Asleif Hamalsdotter is dead. Unlike other items, the bearhead has not been given a graphical update. If lost you can speak to Hamal the Chieftain to obtain another bearhead for free. You do not have to fully complete the quest to equip the bearhead.
The bearhead was fairly popular among pures before the Evolution of Combat, as it had somewhat better stats than the iron full helm, and it could be retrieved without gaining any unwanted experience toward the skills they avoided training, but the stats have been since removed, and now the head is simply a cosmetic item.