The ornamental design for decorative urn, as shown and described.
The claimed ornamental design for an urn which embodies the design is for use as a decorative cremation urn.
The FIGURE is a front elevational view of a decorative urn showing our new design, the color black represents color contrast, the undisclosed portions are not part of the claimed design.
The broken lines in FIG. 1 are for illustrative purposes only and forms no part of the claimed design.