I do not use bookmarks of any sort. I never left a sign on any book ever. I know that if I did that, the ghost of some of my ancestors would come at night and pull my foot.
This note might be useful. If one underlines or marks a book while he is preparing for a test, when he rereads for a higher mark, he is automatically attracted, hence distracted from understanding more. I learned this long time ago. My colleagues and me we got very high marks with 3 readings of a subject, good marks with 2 readings and just passed with one.
I read several (actually many) books at the same time. Obviously my ancestors, of whose ghosts I am so in awe, have left me with an excellent selective memory. When I pick up a book that has rested for a little while, I usually open it at the right place right away. If I resume a reading from a longer time, then I find very pleasurable to retrace where I stopped reading. In this way I get back in the mood. The real problem is with the not so kind person who takes care of the house chores. I think she hates me, maybe because I read so many books and I leave them everywhere, and she usually puts them away in tricky places.