Quick answer: This is a signaling and safety item from Dive Rite.
Being seen at the surface is basic safety, especially in current, boat traffic or open water. Signaling gear is light, compact and easy to carry on every dive.
Check how it clips or stows on your gear, and practice deploying it before you need it. Read The Hidden Risks of Ill-Fitting Gear. More options: Safety & Rescue Products.