The ornamental design for a swab, as shown and described.
FIG. 1 is a perspective view of a swab of the new design;
FIG. 2 is a front view of the invention illustrated in FIG. 1;
FIG. 3 is a rear view of the invention illustrated in FIG. 1;
FIG. 4 is a right side view of the invention illustrated in FIG. 1;
FIG. 5 is a left side view of the invention illustrated in FIG. 1;
FIG. 6 is a top view of the invention illustrated in FIG. 1; and,
FIG. 7 is a bottom view of the invention illustrated in FIG. 1.
The swab is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed invention.