I claim the ornamental design for an advertising display sign, as shown and described.
FIG. 1 is perspective view of an advertising display sign showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a top view thereof.
The dot-dot-dash broken lines shown in FIGS. 3 and 6 illustrate hand slits that form no part of the claimed design. The dot-dash broken lines shown in FIGS. 1 and 2 illustrate a printing region for advertising indicia and forms no part of the claimed design.