The ornamental design for a bookpagemarker, as shown and described.
FIG. 1 is a front view of a book page marker showing my new design;
FIG. 2 is a back view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is a left side view thereof, with the right side view being a mirror image of;
FIG. 6 is a front perspective view thereof;
FIG. 7 is a front perspective view thereof, showing the book page marker inserted into the spine of a book; and,
FIG. 8 is a front view thereof, showing the book page marker inserted into the spine of a book with ribbons inserted for marking multiple pages of the book.
Right side views not shown are mirror images of left side views.
The broken lines shown in FIGS. 7 and 8 represent the environment of the claimed design and form no part thereof.