That's brutal. I can't believe another motorcyclist stole your helmet, probably some punk ass kid taking advantage of an opportunity.
Im gonna guess it wasn't another motorcyclist that did it. Rarely will a biker steal another biker's equipment, unless they aren't really a "biker." Ie, they are just a fucktard on two wheels at the moment. Its exactly the same concept from back in my snowboard days. I, and my friends would frequently leave our $1000 gear outside in the staging area to go warm up or have lunch, because other snowboarders (and skiers) don't steal their brethren's stuff. Ive heard ofthe a deck theif seen riding a board he stole at the same slope. The owner's friends founsf him and a wrong was righted. Its the weekend kids and wannabes that you gotta look out for. In your helmets case, the punk probably has no idea what he got till he goggled it.