If an author is fortunate enough to move up the ranking an arrow will appear in his or her signature and profile. Often the site will also show the number of places that the author moved up the rank.
This author is currently ranked at 45 and has moved up two spots in the ranking.
Generally authors move up the ranking quickly when a well received story or poem is published. A hot story or poem can turn the heat up (indicated by the popularity rating shown in an authors profile).