Is SCN Polar or Nonpolar?

Answer: SCN- is a polar molecule due to the difference in electronegativity between nitrogen (3.04), carbon (2.55) and sulfur (2.58). Partial negative charges will be found closer to nitrogen as it pulls electrons from the other part of the structure containing carbon and sulfur. 

Due to the negative charge on the nitrogen atom, the molecule typically acts more as a "base" in that it is more likely to adopt a hydrogen atom. Being an ion, SCN- commonly forms a wide variety of salts with different alkali metals (such as sodium, potassium) and alkali earth metals (magnesium, calcium). Since there is a relatively small difference in electronegativity between nitrogen and sulfur the molecule is able to donate electrons within a reaction from either end of the molecule. SCN- is also known as Thiocyanate. The molecule is often formed by the addition of Sulfur with Cyanide. 

SCN Ball and Stick Model
SCN Ball and Stick Model. Created with Avagadro.
What is the important role of SCN- within the human body?

SCN- is one of the building blocks of many factors that serve antibacterial functions within the body. These factors have been discovered in many natural defense mechanisms including mucous, saliva and tears. This has been related to the symptoms associated with cystic fibrosis. SCN- inhibits iodine transport into thyroid cells so it is recommended that people who are iodine-deficient avoid foods containing thiocyanate. Once upon a time it was utilized in the treatment of hypertension but it has been since replaced in such function by a closely related molecule.