The ornamental design for a hairbrush, as shown and described.
FIG. 1 is a perspective view of a hair brush showing our new design;
FIG. 2 is an end elevational view thereof;
FIG. 3 is an end elevational view of a second embodiment of the hair brush,
wherein the only difference resides in the fact that this embodiment has
ten instead of twelve parallel rows of projections;
FIG. 4 is an end elevational view of a third embodiment of the hair brush,
wherein the only difference resides in the fact that this embodiment has
eight instead of twelve parallel rows of projections.