The ornamental design for a display apparatus, as shown and described.
FIG. 1 is a front perspective view of a display apparatus showing our new design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is left side view thereof; and,
FIG. 7 is a right side view thereof.
The dot dashed broken lines show unclaimed boundaries which form no part of the claimed design. The oblique shade lines show transparency and not surface ornamentation.