Bookmark. And V. should know that his diary is gone, it was implied Malfoy Sr. told him so.
thats a good thought about hiding a horcrux in one of the former headmaster and headmistress's portraits thats a place where no one would expect but V obviously had access to in his days at hogwarts wat former headmaster or mistress would help out V though? And it could be the sword thats what DD thought it was right? or the hat who knows?