May we suggest:
CJ Recht Subway Ring in Sterling Silver
The Subway ring! Can be used to back people off when they get a little too close to you on the subway….and it will leave a mark. (How do you think it got this name?) Jen Heebner of JCK blogged about this ring in her 360 * Blog this fall.
Shown in sterling silver, the Subway Ring is also available in bronze and blackened sterling silver. And the Subway series includes stud earrings and a pendant too. The Sterling silver Subway ring is 290, 295 if you want it blackened, and the bronze version is 250.