I claim the ornamental design for an advertising display, as shown and described.
FIG. 1 is a front/right-side perspective view of an advertising display showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left side-view thereof;
FIG. 5 is a right side-view thereof; and,
FIG. 6 is a top view thereof.
In the drawings, the broken lines and the subiect matter contained therein are shown for the purpose of providing environmental structure and form no part of the claimed design.