The ornamental design for a pen, as shown and described.
FIG. 1 is a perspective view of my new design for a pen;
FIG. 2 is a side view in elevation of the new design;
FIG. 3 is a side view in elevation of the new design oriented 180 from that shown in FIG. 2;
FIG. 4 is a side view in elevation of the new design oriented at a position 90° from the view depicted in FIG. 3;
FIG. 5 is a side view in elevation from a direction 180° from that depicted in FIG. 4;
FIG. 6 is a top view of the pen; and,
FIG. 7 is a bottom view of the pen.
The broken lines showing features on the inside in FIGS. 1, 2, 3, 4 and 5 are included for the purpose of showing features that form no part of the claimed design.