The ornamental design for a tow tag, as shown and described.
FIG. 1 is a perspective view of a tow tag;
FIG. 2 is a front view thereof;
FIG. 3 is a side view thereof (opposite side is mirror image); and,
FIG. 4 is a top view thereof.
In FIG. 1, the broken line showing of environmental structure for purposes of illustrating the tow tag in a condition of use. The broken lines and the structure they depict form no part of the claimed design.