Unadorned Chain
"Accept this chain, which shall symbolize your duty and your bond as a Liegeman in fealty to the Kingdom. Never forget the burden of this chain."
N. An Unadorned Chain is usually presented to a new Knight as a symbol of fealty. Only knights are allowed to wear unadorned chains.
Traditions
Knight's chains have an basis in medieval and Renaissance traditions. When a knight was created, be in a hereditary title or other wise he was give a chain. The chain was a symbol, tie the man to the land and his liege lord. It was usually gold, and made of heavy intertwined links. It was a cousin to the Necklace, or Chain of Office. In england and france especially there were several different Orders of knights which each had specific chains, like the "Most Noble Order of the Garter".
In Amtgard
In Amtgard chains may be of many colors and are often crafted from chain mail links. Many knights wear chains that also bear the colors of their knighthood, or hoods. Sometimes company or household colors are used.
It is considered highly inappropriate to wear a chain if you are not a knight.