We've talked about some of the moral and ethical considerations that go along with the choice to arm yourself. But even if you are ethically comfortable with carrying a weapon, the Boston legal system may not be so comfortable with your choice. Tony Blauer, President of Blauer Tactical Systems, often reminds students that the final portion of any self-defense situation may involve "you vs. the legal system". If you are going to carry a weapon, that conflict may become a much more difficult one.
This article is no substitute for professional legal counsel; if you have serious questions about the law surrounding your right to bear arms, go talk to a lawyer. Massachusetts' weapons law is quite extensive, and the time to learn about is not when you are talking to an arresting officer.
Firearms, of course, are very strictly and heavily regulated. With the proper licensing, it is possible to carry a concealed firearm. Many other martial arts weapons, including knives, nunchaku, shuriken, manrikigusari, are subject to regulations as well. Mostly, they are illegal.
Under the right circumstances, even a dog can be considered a dangerous weapon.
The penalties for carrying an illegal weapon are far from insignificant (five to seven years in prison), and the penalties for using one are even harsher (depending on how badly you hurt someone with it).
Common wisdom in the self-defense community is that it is "better to be tried by twelve than carried by six." While there may be some truth to that, it's also true that being tried by twelve can be nearly as physically, emotionally, and fiscally draining as an assault. If you are going to make the choice to carry a weapon, make sure that you understand the legal consequences of what you are doing before you do so.