Ranks, or Reputation, is a reflection of how a faction views you. A sufficiently negative reputation means that the faction in question considers you an enemy, will attempt to kill you on sight and is usually marked with red reticules and sector map markers for your visual convenience.
Each rank requires roughly 3 times the points to advance. For each rank you gain, you must do 3 times the work, or do things worth 3 times the notability. Each step is (more or less) geometrically harder than the last.
An “L” displayed in-game after the race's rank indicated the player owns a police license for that faction.