What does N mean after a runway visual range (in a METAR)?
RVR often has a letter at the end to indicate the visibility trend, so you can tell if it's going to improve (and maybe you should circle overhead for a while) or worsen (and you should consider going to your alternate).

U means an "upward" trend: visibility is improving. D means a "downward" trend: visibility is worsening. N means no change.