Wikipedia
A service star is a miniature bronze or silver five-pointed star inch in diameter that is authorized to be worn by members of the seven uniformed services of the United States on medals and ribbons to denote an additional award or service period. The service star may also be referred to as a campaign star or battle star depending on which award is authorized the star and the manner in which the device is used for the award.
Service stars, Campaign stars, and Battle stars are worn with one point of the star pointing up on the suspension ribbon of a medal and or service ribbon. A silver star is worn instead of five bronze stars. A service star is sometimes mistaken for a Bronze Star (Bronze Star Medal) or Silver Star (Silver Star Medal). The service star is also similar to the gold and silver Inch Stars which may be authorized to be worn on specific individual decorations of certain services to denote additional decorations.