Round means the Earth.
Square means Twin Towers.
Golden cross means broken heart.
Ground Zero is written in Braille on the debris underneath.
It is lusterless because of natural color during the process of the work.
Usually, using abrasives and preserving in strong acid may remove oxidized colors in order to show the luster. But, considering the ecology, the natural color may be the much more beautiful. The more you wear, the more brightly it shines.