The ornamental design for a clusterboxindicator, as shown and described.
FIG. 1 is a front elevational view of a cluster box indicator showing our new design, the rear, right, and left side elevational views being identical.
FIG. 2 is a top plan view.
FIG. 3 is a bottom plan view; and,
FIG. 4 is a perspective view thereof showing the bottom, front, and right sides.