The ornamental design for "beak cap," as shown and described.
FIG. 1 is a perspective view of "beak cap" showing my new design
FIG. 2 is a right side elevational view of FIG. 1
FIG. 3 is a perspective view of a second embodiment of "beak cap" which has a hole in the portion showing my new design; and,
FIG. 4 is a right side elevational view of FIG. 3.
The broken line showing of the crown and the visor is for illustrative purposes only and forms no part of the claimed design, and the broken line shown in the solid line on the part of the crown represents stitching.