This article is from the Unicycling FAQ, by Beirne Konarski with numerous contributions by others.
Yes, the unicycle has a front and a back, even when the seat doesn't. The
two pedals are threaded in opposite directions and are normally marked 'L'
and 'R' on the ends of the shafts. The side designation is from the
viewpoint of the rider. Forward riding on either a unicycle or bicycle will
tend to tighten the pedals. However, backward riding on a unicycle will tend
to loosen the pedals.
Also, some tires have a direction on them, due to the tread pattern.
Beirne Konarski firstname.lastname@example.org
Ken Fuchs - email@example.com