The ornamental design for a hairbrush, as shown and described.
FIG. 1 is a top front perspective view of a hairbrush;
FIG. 2 is a bottom front perspective view of the design shown in FIG. 1;
FIG. 3 is a front elevation view of the design shown in FIG. 1, the rear elevation view being a mirror image thereof;
FIG. 4 is a right side elevation view of the design shown in FIG. 1;
FIG. 5 is a left side elevation view of the design shown in FIG. 1;
FIG. 6 is a top plan view of the design shown in FIG. 1; and,
FIG. 7 is a bottom plan view of the design shown in FIG. 1.
The broken lines shown in the drawings depict portions of the hairbrush that form no part of the claimed design.
In FIGS. 2-5 and 7, the use of stippling indicates a contrast in appearance relative to the appearance of the remaining portions of the claimed design.