The ornamental design for a golfballmarker, as shown and described.
FIG. 1 is top perspective view of the ornamental deign;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a right-side elevational view thereof; and,
FIG. 5 is a bottom plan view thereof.
The left-side elevational view and the rear elevational view of the first embodiment are, respectively, identical to the right-side elevational view and the front elevational view of the first embodiment. Thus, the left-side elevational and rear elevational views of the first embodiment are not provided. The broken lines depict environmental subject matter only and form no part of the claimed design.