Final answer:
A Gold Star device is added to a Navy-Marine Corps Achievement Medal ribbon to represent a second award.
Step-by-step explanation:
To signify that an individual has been awarded the Navy-Marine Corps Achievement Medal for a second time, a Gold Star device should be added to the ribbon. The different devices are used to indicate additional awards beyond the first decoration. In the case of the Navy and Marine Corps, subsequent personal decorations are denoted by gold stars. If it were a fifth award, a silver star would be used to represent the previous four awards PLUS the original one. The options like Bronze Star and Silver Star mentioned might be confused with separate medals in the military honors system, but within the context of devices used to indicate multiple awards of the same medal, gold stars are used. The Oak Leaf Cluster is relevant in the Army and Air Force recognition system, not the Navy-Marine Corps.