I think I'd be inclined to disambiguate them by making the ends of the bishop pointed and the ends of the rook blunt. When moving along a diagonal you're moving

I think I'd be inclined to disambiguate them by making the ends of the bishop pointed and the ends of the rook blunt. When moving along a diagonal you're moving in the direction of square corners, vs faces for moving in ranks and files, so it makes sense in that way, and it also evokes the shapes of the classical pieces.