The ornamental design for alignment markings for lens blanks, as shown and described.
FIG. 1 is a front view of alignment markings of our design displayed on a display, the broken line drawing of the display, lens blank, and finished lens shape is for illustrative purposes only and forms no part of the claimed design;
FIG. 2 is a front view of the alignment markings of FIG. 1 displayed on the display in a second orientation; and,
FIG. 3 is a front view of the alignment markings of FIG. 1 displayed on the display in a third orientation.