Are my hands "deadly weapons" when I reach black belt?

Nope, not, no way, ain't happening even if you do makiwara, etc. Now, if you have a willing participant who will stand still and allow you to apply some technique that has a potential to inflict great damage it may or may not actually cause death. It is not that easy to "kill" someone with your hands and feet.

I would tend to believe that if death occurred it was not the technique that does it but rather some other external action or incident that causese the death, i.e. like I hit you in the face and you fall, i.e. gravity is the killing energy here, and hit your head on a rock. The likelihood of death is greater here but this is not fool proof either.

Now, can your karate technique cause damage to another person? You betcha it can but then again the damage may or may not end the incident. There is just too much going on and the probability that your technique will actually kill someone is very, very low. But remember, the damage you do and the circumstances under which you apply said damage can lead to incidents of wrongful death which can be classified and unlawful killing, i.e. murder.

In order to answer this question you will need to touch base with professionals and the associated research to determine just how many killings or death are a result of a martial art technique. Bet you will find none or may one or two and then you will find that the killing/death was a result of something occurring after the application of said technique.

Deadly weapons can be a baseball bat, a carving knife from your family silver set, or a fall from tripping over a newspaper you forgot to remove from the front walk to your front door. Is the probability of this high or low?

Now that I answered the question here is another question that relates, "Are my hands deadly weapons?" The answer is not clear cut but as I find from a recent article you can kill with your hands and feet. Read the article, "Punched to Death." There are FBI details there that do speak to many things regarding hand-to-hand encounters, etc.