The ornamental design for a gravemarker for pet, as shown and described.
FIG. 1 is a perspective view of a grave marker for pet showing my new design;
FIG. 2 is an exploded view thereof;
FIG. 3 is a front view of the grave marker for pet, the rear view being a mirror image thereof;
FIG. 4 is a left side view thereof, the right side view being a mirror image thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dash-dash broken lines in the drawings depict portions of the grave marker for pet that form no part of the claimed design. The dot-dot-dash showing of the rectangular top piece in the drawings depicts environment, that forms no part of the claimed design.