The ornamental design for a signframe, as shown and described.
FIG. 1 is a rear elevation view of a sign frame showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a left side elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a rear perspective view thereof;
FIG. 8 is a front perspective view thereof; and,
FIG. 9 is another rear perspective view thereof.
The broken lines of the waste bin are directed to environment and are for illustrative purposes only. The broken lines form no part of the claimed design.