Claimed is the ornamental design for the sling device, as shown and described.
FIG. 1 is a top, front, left side perspective view of a sling device.
FIG. 2 is a front elevational view thereof.
FIG. 3 is a rear elevational view thereof.
FIG. 4 is a left side elevational view thereof.
FIG. 5 is a right side elevational view thereof.
FIG. 6 is a top plan view thereof.
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a top, rear, right side perspective view of the sling depicted with its environmental subject matter.
The claimed design shows vertical and horizontal breaks. The appearance of any portion of the article between break lines forms no part of the claimed design. The broken lines showing a human figure and logs are for the purpose of illustrating environment and form no part of the claimed design.