The ornamental design for a packingbox, as shown and described.
FIG. 1 is a front perspective view of a packing box showing our new design in a closed configuration;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is top plan view of the packing box, showing our new design in a flat configuration.
In FIGS. 1, 2, and 8, the shape on the front surface of the article defined by three broken lines and one solid line adjacent to the shaded planes depicts a portion of the packing box that forms no part of the claimed design. All the sides except the front side depict portions of the packing box that form no part of the claimed design.