The ornamental design for a signholder, as shown and described.
FIG. 1 is a front, top, and right perspective view of a sign holder in accordance with the present disclosure;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a top plan side elevation view thereof;
FIG. 5 is a bottom plan side elevation view thereof;
FIG. 6 is a front elevation view thereof;
FIG. 7 is a back elevation view thereof; and,
FIG. 8 is a back, top, and right perspective view thereof.
In the drawings, the broken lines depict unclaimed subject matter only and form no part of the claimed design. The separation and brackets indicate that the precise length of the sign holder is not claimed.