The ornamental design for an warningsign, as shown and described.
FIG. 1 is a perspective view of the warning sign in the flat orientation;
FIG. 2 is a top view of the warning sign;
FIG. 3 is a bottom view of the warning sign;
FIG. 4 is a front view of the warning sign;
FIG. 5 is a back view of the warning sign;
FIG. 6 is a side view of the warning sign;
FIG. 7 is a side view of the warning sign; and,
FIG. 8 is a perspective view of the assembled device on a shipping container.
In the drawings, the dotted broken lines represent perforations. The dashed broken lines showing text on the warning sign and a shipping container illustrate environment and form no part of the claimed design.