BMW Motorrad lockable "Safety" oil filler cap, also known as a safety screw for the oil filler neck. It is a security and anti-vandalism accessory for most R1200 and R1250 Boxer engine models. 
Features and function
Theft and vandalism prevention: The cap replaces the standard plastic oil filler plug. It requires a special, uniquely shaped key to be opened, which prevents unauthorized access to your engine's oil system.
Protection against contamination: By locking the oil filler, it also blocks the entry of foreign substances that could contaminate the engine oil.
High-quality construction: The cap is milled from solid aluminum, features "BMW Boxer" lettering, and includes a new O-ring seal.
Simple installation: It is designed to be a straightforward replacement for the stock oil filler plug