We claim the ornamental design for a crescent button overlay for a virtual keyboard, as shown and described.
FIG. 1 is an elevation view of the front side of the crescent button overlay for a virtual keyboard, arranged over a device rendering a virtual keyboard;
FIG. 2 is a right side isometric view of the front of the crescent button overlay for a virtual keyboard, thereof;
FIG. 3 is a side elevation view of the crescent button overlay for a virtual keyboard, thereof;
FIG. 4 is a elevation view of the front side of the crescent button overlay for a virtual keyboard, thereof, shown without the rendered virtual keyboard and display screen frame for clarity of disclosure; and,
FIG. 5 is a top-right side isometric view of the front side of the crescent button overlay for a virtual keyboard, as shown in FIG. 1.
The broken lines in the Figures show portions of the crescent button overlay for a virtual keyboard, which form no part of the claimed design.