I claim the ornamental design for a shirt stay, as shown and described.
FIG. 1 is an elevated perspective view of a shirt stay according to my new design.
FIG. 2 is a right side view and the left side (not shown) is a mirror image thereof;
FIG. 3 is a bottom view thereof with the fabric of the shirt stay laid in a flat plane as if on top of a table;
FIG. 4 is a top side view thereof with the shirt stay laid in a flat plane as if on top of a table;
FIG. 5 is a back end perspective view thereof; and,
FIG. 6 is front end view thereof with the shirt stay laid in a flat plane as if on top of a table.
The four fabric clasp structures extending from the corners of the shirt stay and shown in dashed lines do not form part of the claimed subject matter in FIGS. 1-6. In FIGS. 1-6 the dashed lines that show features other than the four fabric clasp structures extending from the corners of the shirt stay are intended to show stitching and do form part of the claimed subject matter.