The ornamental design for a headerornament, substantially as shown and described.
FIG. 1 is a raised perspective view of a header ornament showing my new design;
FIG. 2 is a front view of the header ornament of FIG, 1;
FIG. 3 is a rear view of the header ornament of FIG. 1;
FIG. 4 is bottom view of the header ornament of FIG. 1;
FIG. 5 is a top view of the header ornament of FIG. 1;
FIG. 6 is a left-side view of the header ornament of FIG, 1; and,
FIG. 7 is a right-side view of the header ornament FIG. 1.
The broken lines shown in the drawings form no part of the claimed design. The surface shading illustrated in the drawings is provided merely to highlight the contour of the design and is not part of the claimed design. All surfaces not shown form no part of the claimed design.