The ornamental design for a fingerbrush, as shown and described.
FIG. 1 is a perspective view of a finger brush showing my new design;
FIG. 2 is a side view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a reduced perspective view thereof shown mounted on the finger of a user's hand.
The broken lines showing a user's hand are for illustrative purposes only and form no part of the claimed design. The broken line structure projecting from the bottom of the article illustrates a portion of the finger brush that forms no part of the claimed design.