For runners, cyclists, and skaters, the Runbell provides the option of giving pedestrians and other manual motorists in your path polite notice of your presence and passing. So you don't have to yell at them, plow them over, or use your little ding-ding!-ing knuckle duster as it was originally intended to get them to move the F out of the way.
I can't look at the Runbell without laughing. Sure, it's not a full four-knuckled duster, but even as a double knuckler, it's ironic and amusing to see the Share-the-Road world's reassignment of a hardcore, and often illegal, weapon as a tool of etiquette and safety. Maintaining its nod to gangsta smackdowns, the Runbell comes in Gold and Copper. You can also pick from men's and women's finger sizes.