The ornamental design for a hairbrush, as shown and described.
FIG. 1 is a perspective view showing my new design for a hair brush;
FIG. 2 is a front elevational view thereof; the rear elevational view, the left side elevational view and the right side elevational view being a mirror image thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a perspective view showing the head of the hair brush changed to second appearance;
FIG. 6 is a front elevational view of another appearance thereof; the rear elevational view, the left side elevational view and the right side elevational view being a mirror image of second appearance thereof;
FIG. 7 is a top plan view of second appearance thereof; and,
FIG. 8 is a bottom plan view of second appearance thereof.
The portions shown in broken lines are included for illustrative purposes only and form no part of the claimed design.