I claim the ornamental design for a coupon binder, as shown and described.
FIG. 1 is a perspective view of a coupon binder, showing my new design;
FIG. 2 is a perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left-side elevational view thereof;
FIG. 6 is a right-side elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines showing text and a flower design in FIGS. 1 and 3 and papers in a pocket of the design in FIG. 2 depict environmental matter and form no part of the claimed design. The remaining broken lines on the design represent stitching that form a part of the claimed design.