If you see an attacker coming and pull a knife, don't pull it for show. You pull it to use it. Anything else is a waste of time. Now having said that, if you pull a knife, you better damn well be versed in its use and the ramifications of that use, including personal morals and legalities. Hopefully you will not have to use the knife, but never pull one without the express purpose of using it. Don't ever carry a weapon for ego, as that is the fastest and easiest way to either get yourself hurt and/or in trouble with the law. There are different ways to use a knife. Whichever ways you have trained and are comfortable with are the ways you should use it.