Yes. You can bring autograph books, pillow cases, photo mats etc, and GS will get it signed.They will give you or fill out for you a sheet of paper, that as the available characters and ask which ones you want, and also name and cabin number.
GS is located Deck 3 amidships, port side of the atrium.(When you board the ship, walk to the opposite side of the ship, and turn right youll be standing infront of the desk.)
As a suggestion, and a thank you, most people will leave a small bag of candy with gs to go to the entertainment staff.Also, when we did it in August, we dropped off the 2 autograph books, the first night on the ship, and it was delivered to our cabin on the last night, ready to go.