Final answer:
Upon receiving a second sea deployment ribbon, a bronze service star should be attached to the existing ribbon to denote the additional award.
Step-by-step explanation:
The subject of this question is concerned with military awards, specifically the protocol for indicating multiple awards on a uniform ribbon. In the U.S. military, upon receipt of a second sea deployment ribbon, the correct device to attach to the existing ribbon is a bronze service star.
A service star is used to denote subsequent awards when a member receives a medal, ribbon, or badge more than once. When a third award is received, a second bronze service star is added, and so on. For Navy and Coast Guard personnel, a silver service star is added in lieu of five bronze stars. This practice of indicating multiple awards helps to maintain the uniform appearance and the traditional way of recognizing and displaying military honors.