The ornamental design of a golf putter head, as shown and described.
FIG. 1 is a rear perspective view of a golf putter head showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a left side elevational view thereof, the right side elevational view being the mirror image thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken line showing of a fragmented shaft is for illustrative purposes only and forms no part of the claimed design.