Regards...
I'm thinking that I should share some things with you my friend (husnira)
In the USA where I and some other members live it is VERY ILLEGAL to cut someone for the purpose of warning them of your superior skill with weapons.
In the USA a knife is one of several so called "deadly" weapons. So if you use any deadly weapon to simply sever the fingers or cut on the brow as a warning you can go to jail for a long time. In the USA self defense with a weapon pre suposes the intent of the aggressor is serious bodily harm or death so we do not have the legal obligation to warn our attacker at all.
One of a handfull of silat men here in the USA teach edged weapon
defense to police officers and civilians but he is American and understands the laws of our land and the issue of using deadly force to defend against armed assaults. We must be in IMMEDIATE fear of "Serious" injury or death to use a weapon for self defense at all.
We can't even own police batons but guns are okay... Go figure that one out!
While I support your moral obligation to give every opportunity to the attacker to change his mind I would suggest that your attacker seldom holds such values.
All the best!
Ray