Asthetic attributes aside, a piece of jewelry can signal taste, affiliation, availability or memberhip.
Jewelry often plays the role of benchmark or milestone. Wedding and engagement rings, school rings and service pins commorate commemorate life's benchmarks and milestones. As friends began to turn 50, I wanted to mark their 1/2 (.5) century on the planet: award them for time served with a small badge of honor. The club has grown to include .25's and a few .6's and sometimes five or six pins show up at an event.
Milestones can be made to order as pins or pendants and even belt buckles.