We claim the ornamental design for an sink apron, as shown and described.
FIG. 1 is a top, front, right perspective view of an embodiment of the claimed design;
FIG. 2 is a front elevation view thereof; and,
FIG. 3 is a partial cross-sectional view taken along lines 19-19 in FIG. 2.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. Broken lines formed by equal length dashes show unclaimed subject matter. Broken lines formed by unequal length dashes (i.e., dash-dot) define bounds of the claimed design. Broken away symbols having a jagged element show that no particular length of the portion is claimed. Portions of the claimed design having line shading and stipple shading define contrasting surfaces.