Martial Arts is a secondary ability that adjoins to the Brawl Ability, and adheres to the rules for secondary abilities. In order to have a 3 in martial arts, one must have a brawl rating equal to or higher.
The various styles of Martial Arts will give special bonus' and difficulty changes. For each dot of Martial Arts, a character will have a maneuver that will enhance their combat ability.
For example, Tink's character has a Martial Arts rating in Karate. As a special move, her kick attacks are at a -1 difficulty to perform.
A character with Krav Maga, has a -2 difficulty to disarm her foe.
The list is far from complete, and its being worked out, if any character wishes to learn a martial art form, speak with an ST about moves for that martial art.