The ornamental design for a three sided display holder, as shown and described.
FIG. 1 is a pictorial view of a three-sided display holder showing our new design, with the broken lines showing being for illustrative purposes only and forming no part of the claimed invention;
FIG. 2 is a side elevational view of one side of the design shown by FIG. 1, with a center portion broken away for the purpose of shortening the view, such view illustrating each of the three sides of the display holder because the three sides are substantially identical, and further directly showing the side appearance of the display holder when it is vertical, and further showing the side appearance of the display holder when it is horizontal, by merely rotating the figure ninety (90°C) degrees and then viewing it, such view also including broken lines for illustration purposes only and forming no part of the claimed invention; and,
FIG. 3 is an end view of both ends of the design, such view also including a broken line showing for illustration purposes only and forming no part of the claimed invention.