The ornamental design for a supportingstand for a display, as shown and described.
FIG. 1 is a perspective view of a supporting stand for a display showing my new design;
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; and,
FIG. 7 is a bottom plan view thereof.
The evenly spaced broken lines that are immediately adjacent to the shaded area and define unshaded regions depict the bounds of the claim. All broken lines form no part of the claimed design.