The ornamental design for a scissors holder, as shown and described.
FIG. 1 is a right side elevation view of a scissors holder showing my new design, the broken line disclosure of a scissors being for illustrative purposes only and forming no part of the claimed design with the left side being a mirror image of that shown;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is a front right side perspective view thereof.