The ornamental design for diamond with inscribed cross, as shown and described.
FIG. 1 is a top view of a diamond with inscribed cross showing my new design;
FIG. 2 is a front view of FIG. 1, with the rear view being symmetrical; and,
FIG. 3 is a side view of FIG. 1, with the other side being symmetrical.
The broken line showing of a setting in FIGS. 2 and 3 is included for the purpose of illustrating environmental matter and forms no part of the claimed design.