Many asexuals wear a black ring on the middle finger of their right hand. The material and exact design of the ring are not important as long as it is mostly black. Some wearers use hematite rings because they are inexpensive and fairly easy to find.
The origin of the black ring symbol can be found in this thread started in 2005.
|Your right middle means "currently single", the right ring means "currently taken" and since the left ring means "taken/married" in a permanent sense, then the next logical conclusion would be that left middle means "permanently single".|