I claim the ornamental design for a display screen stand, as shown and described.
FIG. 1 is a perspective view of a display screen stand, showing my new design;
FIG. 2 is an exploded perspective view thereof;
FIG. 3 is a front elevational view thereof, the rear elevational, left-side elevational, and right-side elevational views all being a mirror image thereof;
FIG. 4 is a top plan view thereof; and,
FIG. 5 is a bottom plan view thereof.
The broken lines in FIG. 5 depict environmental matter, and form no part of the claimed design.