Originally Posted by fietsbob

rare, but there were Self Energizing U brakes , which were directional ,
because of the internal mechanism, a coil spring, and helix..

as the pad hits the rim the motion pulls the helical follower tighter on the rim..

Then which way it faced, matters a lot..

NB: Though on the rear, if the mounting is below the chainstays,
then functionally it is like a front brake, on the trailing side of the rotation of the wheel.