The ornamental design for a mirror, as shown and described.
FIG. 1 is a perspective view of an ornamental design for a mirror showing my new design;
FIG. 2 is a front orthographic view thereof;
FIG. 3 is a rear orthographic view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a left side view thereof.
The broken lines shown in FIGS. 1–6 are included for the purpose of illustrating environmental elements only and form no part of the claimed design. The bottom view is omitted and forms no part of the claimed designs.