The ornamental design for a proximitymarker, as shown and described.
FIG. 1 is a front elevation view of a first embodiment of a proximity marker of the present invention;
FIG. 2 is a rear elevation view thereof;
FIG. 3 is a right side elevation thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a top view thereof, and,
FIG. 6 is a bottom view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. Any broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.