I was always under the impression, Sikorski was a kaszub name. My greatgreatgrandmother was a Sikorska. In an old Kartuzy book the Sikorski name shows up as Sikorra, Szikora. There is also a town of Sikorshyn in the Kashub area. Usually people adopted their last name from the place they lived at, once the tribal name was dropped. Some kaszub families carry three names, the tribal name, the place and the polish name.