Nostrildamus' Medallion is a mythical artifact that allows its user to look into the near future.
According to legend, Nostrildamus' medallion would transfer the powers of Nostrildamus to anyone who wore it. However, it had a terrible curse placed on it.
Scrooge wore it and soon realized that although the medallion itself could allow him see into the future, all he could see would be the perils originated by the ccurse placed on the medallion.
For that reason, Scrooge was forced to return the medallion back to its original location.