A rare gold coin was donated to a Salvation Army Red Kettle in Washington, Pennsylvania, by an anonymous good Samaritan due to holiday foot traffic. Coin expert weighs in.

Look for hallmarks. All authentic gold bars and coins have a hallmark stamp that indicates their purity. This stamp is a guarantee from a reputable manufacturer that the gold is 100% pure.

For example, the 1933 Double Eagle gold coin, minted but never legally circulated, is considered government property and therefore illegal to own. In fact, ...