The ornamental design for a bookmark, as shown and described.
FIG. 1 is a front view of my new, original, and ornamental design for a bookmark;
FIG. 2 is a rear view of the bookmark of FIG. 1;
FIG. 3 is an enlarged top view of the bookmark of FIG. 1;
FIG. 4 is an enlarged bottom view of the bookmark of FIG. 1;
FIG. 5 is a perspective view of the bookmark of FIG. 1;
FIG. 6 is a front perspective view of FIG. 1, shown with environment and the ribbon in an alternate position of use;
FIG. 7 is a rear perspective view of FIG. 1, shown with environment and the ribbon in an alternate position of use; and,
FIG. 8 is a side view of the bookmark of FIG. 1.
The broken line showing of details in FIGS. 1-8 is included for the purpose of showing environmental portions of the bookmark and forms no part of the claimed design.
A specific length to the top portion of the bookmark forms no part of the claimed design.