The ornamental design for a medallion, as shown and described.
FIG. 1 is a perspective view of a medallion, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof, the rear elevational view, left-side elevational view, and right-side elevational view all being identical thereto; and,
FIG. 4 is a cross-sectional view thereof, taken along line 4—4 of FIG. 2.
The broken lines showing a roman numeral in the figures depicts portions of the medallion that form no part of the claimed design. The bottom plan view forms no part of the claimed design.