The ornamental design for wearable novelty sign, as shown and described.
FIG. 1 is a front elevational view of a wearable novelty sign;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a first front perspective view; and,
FIG. 4 is a second front perspective view.
The broken lines showing the head of a model wearing the wearable novelty sign are for illustration purposes only and form no part of the claimed invention.