The ornamental design for a clip for writinginstrument, as shown and described.
FIG. 1 is a perspective view of the invention;
FIG. 2 is a back view of the invention;
FIG. 3 is a side view of the invention;
FIG. 4 is a front view of the invention;
FIG. 5 is another side view of the invention, showing the side opposite that shown in FIG. 3;
FIG. 6 is a top view of the invention; and,
FIG. 7 is a bottom view of the invention.
The writing instrument shown in broken lines in the drawings of FIGS. 1-7 is included for the purpose of showing portions that form no part of the claimed design.