Chin spoiler for the BMW GS helmet. It is an original BMW accessory for motorcycle riders. 
Key details about the part:
Description: Chin spoiler, helmet GS.
Product type: An accessory designed to attach to a BMW GS series motorcycle helmet. It likely improves aerodynamics or reduces wind turbulence.
Compatibility: To ensure compatibility, you must verify that the part number is correct for your specific GS helmet model. Retailers often recommend providing your helmet details to confirm the fit.