The ornamental design for an anti-fog mirror, as shown and described.
FIG. 1 is a left perspective view of an anti-fog mirror showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof (the broken lines illustrate non-claimed subject matter and form no part of the claimed design);
FIG. 4 is a left side view thereof (right side view is a mirror image thereof);
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof; and,
FIG. 7 is a right perspective view thereof (the broken lines are directed to environment, and are for informational purposes only and form no part of the claimed design).