A person born under the Thief birthsign is granted a 10-point bonus to Agility, Speed, and Luck attributes. These bonuses are temporary, once the respective attributes reach 100 this sign has essentially no effect. Best fit for a stealth gameplan.
The Thief provides the biggest attribute boost in the game. No other skill modifies Luck so boosting your Luck is a valuable asset for characters who like that skill. Luck affects the Marksman skill, and Mastery perks as well as pickpocketing and sneaking. Choose this birthsign along with Luck as a favorite attribute, and you can easily get your luck up to 100.