I claim the ornamental design for a label for a box, as shown and described.
FIG. 1 is a perspective view of a label for a box, showing my new design.
FIG. 2 is a top view of the claimed design.
FIG. 3 is a right view of the claimed design.
FIG. 4 is a left view of the claimed design.
FIG. 5 is a rear view of the claimed design.
FIG. 6 is a front view of the claimed design.
FIG. 7 is a bottom view of the claimed design; and,
FIG. 8 is a perspective view of a label for a box shown in an environment of use.
The broken lines showing text and fold lines are environmental matter forming no part of the claimed design. The broken lines appearing on FIG. 8 of a box are environmental matter forming no part of the claimed design.