BMW GS helmet. It is specifically for the size 2 (60-63 cm) version of the helmet. 
This is a genuine BMW Motorrad accessory, not a car part. The "collar" in your query likely refers to this "end cover" or "collar section" of the helmet, which provides a clean and finished look at the rear. 
Key details
Part Name: End Cover, Rear Helmet GS
Alternate Name: Collar Section, GS Helmet
Fits: GS Helmet, Size 2 (60-63 cm)
Manufacturer: Genuine BMW