The ornamental design for a tampon, as shown and described.
FIG. 1 is a perspective view of a tampon;
FIG. 2 is a front view of the tampon of FIG. 1, wherein the back view is identical to FIG. 2;
FIG. 3 is a top view of the tampon of FIG. 1; and,
FIG. 4 is a bottom view of the tampon of FIG. 1.
The evenly spaced broken lines shown in FIGS. 1, 2, and 4 illustrate portions of the tampon that form no part of the claimed design. The dash-dot-dot-dash broken lines shown in FIG. 4 illustrate boundaries of the tampon that form no part of the claimed design.