The ornamental design for a decorativebow, as shown.
FIG. 1 is a top plan view of a decorative bow according to my new design;
FIG. 2 is an end elevational view thereof; and,
FIG. 3 is a bottom plan view thereof.
The ribbon coil portions that would be partially visible through the mesh loops have been omitted for clarity; and coil portions not illustrated in the views form no part of the claimed design.
The partial cross hatching representing a mesh material is understood to continue throughout the surfaces of the loop elements of the design.