I don't like to "brag" about having a knife like that.
For one, there is the possibility that someone who is ignorant to the fact I killed a T will kill me, thus ruining both the chance for to gain more karma and ruining his karma.
Second, I don't like to let the other traitors know I have a knife. They'll be more cautious if they do know, and most likely will target me first.
Along with it ruining people's karma, having your knife out just isn't smart at all..