Sticky note bookmark
Everyone knows it, the bookmark slips out. Some also spoil the good books and kink dog-ears, or the like. Much easier and super practical is the use of self-adhesive sticky notes from the block.
It sticks where it should, does not fall out, can be stuck at any time again without any backlog or damage of the sides to the appropriate side. And as an encore: Anyone who has problems memorizing the people in the book can now take notes on it.