The ornamental design for a strikingface for a golf putter head, as shown and described.
FIG. 1 is a perspective view of a striking face for a golf putter head, showing my new design;
FIG. 2 is a front elevational view of the invention;
FIG. 3 is a left-side elevational view of the invention, the right-side elevational view being a mirror image thereof;
FIG. 4 is a top plan view of the invention; and,
FIG. 5 is a bottom plan view of the invention.
The broken lines showing a golf putter body in the figures are included for the purpose of illustrating the invention formed into a typical golf putter body, and form no part of the claimed design.