One Discworld book recounts how Ankh-Morpork Patrician Olaf Quimby II had his reign ended when he was killed by a disgruntled poet during an experiment to test the truth of the saying "The pen is mightier than the sword". In his memory, the saying was amended to read: "The pen is mightier than the sword only if the sword is very small and the pen is very sharp."
Tactical pens sold by many self-defense websites are designed to be much more durable than a garden-variety ballpoint pen so they can be used more effectively as a stabbing weapon. And they write! Actually, any blunt, strong-built pen or marker, even if that pen is not a tactical pen, can be used as a Kubotan or Yawara stick.