The ornamental design for a viewingaid for a visual content source, as shown and described.
FIG. 1 is a top, front right side perspective view of the viewing aid for a visual content source shown in an open position and coupled to an e-reader as in use;
FIG. 2 is a top plan view of the open viewing aid by itself;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a rear elevational view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a top plan view of the viewing aid in a closed position;
FIG. 9 is a front elevational view thereof;
FIG. 10 is a left side elevational view thereof, the right side view being a mirror image thereof;
FIG. 11 is a rear elevational view thereof; and,
FIG. 12 is a bottom plan view thereof.
The broken lines shown in the drawings represent portions of the viewing aid for a visual content source that form no part of the claimed design.