CLAIM The ornamental design for a blackout mask cover, as shown and described.
FIG. 1 is a front view of a blackout mask cover showing my new design, the rear view being a mirror image thereof;
FIG. 2 is a right side view of the blackout mask cover, the left side view being a mirror image thereof;
FIG. 3 is a top view of the blackout mask cover;
FIG. 4 is a bottom view of the blackout mask cover; and,
FIG. 5 is a perspective view of the blackout mask cover shown in a used condition covering the face mask of a fireman wearing a self-contained breathing apparatus, wherein the fireman and the breathing apparatus are depicted in broken lines.
The broken line showing of a fireman and breathing apparatus shown in FIG. 5 is included for the purpose of illustrating environmental structure and forms no part of the claimed design.