The ornamental design for a smart watchcase, as shown and described.
FIG. 1 is a front elevational view of a smart watch case showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a perspective view thereof; and,
FIG. 8 is a perspective view in the state of use.
The long-dash broken lines show portions of the smart watch case that form no part of the claimed design. In FIG. 8, the short-dash broken lines show environment that forms no part of the claimed design.