The ornamental design for a decorativeyarn, as shown and described.
FIG. 1 is an upper perspective view of the decorative yarn showing my design.
FIG. 2 is a front elevation view thereof;
FIG. 3 is a back elevation view thereof;
FIG. 4 is top plan view thereof; and,
FIG. 5 is a bottom view thereof.
The decorative yarn is shown broken away at its ends in order to indicate that a specific length is not claimed, it being understood that the pattern is repeated uniformly through the length.
Elevation views of the sides are not shown and are understood to form no part of the claimed design.