The cones or triangles at the top of a cardinal buoy are very important. The Low Lee buoy is an east cardinal buoy. This tells the master to steer to the east side of the buoy and thus gain safe passage. You'll notice the cones are pointing away from each other.
Incidentally a west cardinal buoy would have the lower triangle pointing straight up and the upper triangle pointing straight down - forming a "waist" type shape.
. A northerly cardinal buoy would have its two triangles pointing straight up.
To read more about the Runnelstone please see here