The ornamental design for a skinmarker, as shown and described.
FIG. 1 is a top plan view of a skin marker and showing the design;
FIG. 2 is a bottom plan view of the skin marker of FIG. 1, the bottom surfaces of which form no part of the claimed design;
FIG. 3 is a front elevational view of the skin marker of FIG. 1, the rear elevational view being identical to the front elevational view; and,
FIG. 4 is a right side elevational view of the skin marker of FIG. 1, the left side elevational view being identical to the right side elevational view.
In the drawings, the broken lines are included to illustrate portions of the skin marker that form no part of the claimed design. The broken lines form no part of the claimed design.