We claim the ornamental design for an portable display device with icon, as shown and described.
FIG. 1 is a side perspective view of an portable display device with icon; and,
FIG. 2 is a front view of the portable display device with icon of FIG. 1.
The evenly spaced broken lines shown in the figures are included for the purpose of illustrating environmental elements and form no part of the claimed design. The dot-dash broken lines illustrate a display screen and form no part of the claimed design.