Commonly called the Mondain Coin or the 300th Anniversary Coin this item was given out to all players to commemorate the 2nd anniversary of Ultima Online in 1999.
The Avatar defeated Mondain and shattered the Gem of Immortality, thus splitting Sosaria into several copies of the same world, or shards. The coin commemorates 300 years since that event. This is a mild matter of conjecture since Sosarian Time moves twelve times faster than Earth time and Ultima Online was only celebrating it's 2nd Anniversary. Either the date calculation is incorrect or the lore points to an earlier date in Earth time of when the shards were first split prior to the launch of Ultima Online. Or it could describe Mondain's original defeat at the hands of Lord British at the end of Akalabeth.
When double-clicked, the coin will display either Ankhs(heads) or Serpents(tails). Due to it's age and moderate scarcity, it is considered an low-level rare item.
When single clicked, it merely displayed the coin's description, "In Commemoration of the 300th anniversary of Mondain’s defeat" prior to the release of Ultima Online: Age of Shadows. After UO:AoS was introduced, including item properties display views, the coin was bugged for a short time and the description was cut off at the end. A later patch changed the description to simply be the slightly changed inscription of "In Commemoration : The 300th Anniversary Of Mondain’s defeat"