Interesting topic. I do carry a "weapon", but it is mainly for wildlife. I don't care to be on the bottom end of the food chain and I'll be damned if I am going to wind up as bear poop on the side of a mountain. So, when I go out into the wild, I carry a canister of bear pepper spray. It's enough to put down a small riot. Last week, I found myself being stalked by two coyotes. I had the spray with me. While I did not think much of it at the time, I did read later that they can be somewhat unpleasant if you're around their den. And, sure enough, I believe I was close to the den. Whatever, I got some good pix out of the encounter.
Oh, and I do carry a nice Swiss army knife with me. Not for the blade and tools, but for extra wallop if I need to clobber someone. I spend plenty of time in Pioneer Square and the surrounding downtown Seattle area. If anyone knows this area, you'll know exactly what I'm talking about.