This self-defense tool by Tooto slips over two fingers, creating a small knuckle duster. It’s made of a titanium alloy and weighs under an ounce.
I’m not sure if it’s effective. The spikes are curved inward, rather than toward a target. But Batman is more than just a man in a batsuit--he’s Batman even without it. If you can use a tool shaped like the Batman logo effectively, then you get to be Batman.
-via Dude I Want That
It doesn't look like a practical weapon, so it would be far from my first choice.