The notch in kukri had many traditional and practical purpose.
According to traditional belief, the notch near the handle of the blade is a Hindu fertility symbol. It is also the footprint of a cow. So the notch forbids slaughtering sacred animal such as cow with it. The Gurkhas also kept promises with it that they will never use this weapon on women and children.
Nevertheless, the knife being a lethal weapon, the notch on it is for the blood to drip off rather than running onto the handle, and thereby prevent the handle from becoming slippery, so the user can maintain his grip for further demonstration.The other most important thing about this is no other knife has this distinctive character in them and only kukri is the design where we can find notch.