Nolan have introduced the helmet lock T-Bar.  It is a 2 mm thick stainless steel plate that slips through the Microlock bayonet catch so you can secure almost any helmet that doesn't have 'D' rings.

Use with Givi's S220 pocket sized retractable high tensile steel cable combination lock for a low cost way to secure your helmet to your bike.

Motorcycle / Motorbike Helmets