A dense, blunt, pole about three feet long ending in a sharp spike on the top, mounted to a handle like a sword. Basically, a spike-baton. I dislike the use of lethal force unless necessary, so the sword-baton-thing would be used to subdue someone, block or break weapons, and then if it turned out they were a bit too determined, spear them on the end.
If the baton can someone sink into the hilt for easy transportation, this would also be a cool thing. Hell, if the baton-sword-thing can emit electricity, then I've found my baby.