The ornamental design for a coin display case, as shown and described.
FIG. 1 is a perspective view of a coin display case showing my new design;
FIG. 2 is an environmental front elevational view thereof; and,
FIG. 3 is a top plan view with the left and right sides and bottom being mirror images thereof.
The broken line showing of the quarter in FIG. 2 is for illustrative purposes only and forms no part of the claimed design. The rear view is plain and unornamented. The lines throughout the figures are simulative of woodgrain and do not represent a particular pattern.