The ornamental design for a hand warmer, as shown and described.
FIG. 1 shows a perspective view of a hand warmer.
FIG. 2 shows a top view of a hand warmer.
FIG. 3 shows a back view of a hand warmer.
FIG. 4 shows a bottom view of a hand warmer.
FIG. 5 shows a right side view of a hand warmer.
FIG. 6 shows a front view of a hand warmer; and,
FIG. 7 shows a left side view of a hand warmer.
Two types of broken lines are used in the drawings, short-dash broken lines and long-dash broken lines. There are short-dash broken lines that depict a hand, part of an arm, and a small rectangular tag-like feature near the wrist end of the hand warmer. Short-dash broken lines are directed to environment or portions of the article and are for illustration purposes only. Short-dash broken lines form no part of the claimed design. There are long-dash broken lines depicting stitching on the hand warmer. Long-dash broken lines are directed to surface indicia and are for illustration purposes only. Long-dash broken lines form no part of the claimed design.