I live in one of those "rough neighborhoods" and I keep my camera with me most everywhere I go. I rarely have a problem, and trust my instincts for when it's okay to have the camera out, and when I'm better off letting it stay in the bag. I'd advise against a weapon of any sort, for the simple reason that unless you shoot your camera one handed, and that with your non-dominant hand. You cannot get to a weapon to use it quickly and with control, and an uncontrolled weapon (gun, knife, pepperspray, sock-full-of-pennies) is more dangerous to you than to someone who has already decided to make themselves a problem for you. If they come as a surprise, you don't have time to get to your weapon, and if they don't come as a surprise, you should've already gotten the heck out of dodge.
People have been shot less than 20 yards from my door, but I'm still more afraid of getting my camera stolen when I'm near work (Michigan Ave).