I claim the ornamental design for a seat belt cushion, as shown and described.
FIG. 1 shows a perspective view of the front side of the seat belt cushion. The rear of the seatbelt cushion in broken lines is not claimed.
FIG. 2 shows a perspective view thereof also showing in broken lines non-elements consisting of a seat belt, pen, gum and phone. The rear of the seatbelt cushion in broken lines is not claimed; and,
FIG. 3 shows a perspective view thereof unfolded as the device might be configured for storage.