The ornamental design of a sensor, as shown and described.
FIG. 1 is a top view showing the ornamental design of a sensor in accordance with the present invention;
FIG. 2 is a perspective view of the embodiment of FIG. 1;
FIG. 3 is a side view of the embodiment of FIG. 1;
FIG. 4 is a bottom view of the embodiment of FIG. 1; and,
FIG. 5 is a bottom perspective view of the embodiment of FIG. 1.
It should be noted that the text in FIGS. 1 and 2 and the bottom surfaces of the device illustrated in FIGS. 2, 3, 4 and 5 form no part of the claimed ornamental design of the present invention and are therefore illustrated in broken lines.