For the past 3 years, I've always had a camera mounted to the right side of my helmet. Got pulled over for it a week or so back for the first time ever, no ticket fortunately as the cop was also a rider and personally supports helmet cams for security/insurance, but he had to warn me that it's technically a traffic law violation and if another cop was having a bad day, it'd be a ticket. (I have always known this, but it's not generally enforced.) The same goes for any kind of helmet "mod" that projects more than 10mm from the surface, so even things like the Scala headsets might technically be illegal, but I've never heard of anyone getting a ticket for those (yet).
As a precaution, I don't ride with my helmet cam mounted in that area anymore, and I now have my secondary GoPro mounted just behind my windshield on the V-Strom, which gets a great view of the road/vehicles directly in front of me, but isn't particularly interesting from a vlogging/"my view" perspective. It's mostly there for safety/insurance purposes anyways, so it's still functional. I'm looking into running a dedicated miniUSB charging line to it so I can effectively use it as a dash-cam and just leave it on constantly while riding. If only the GoPro2 had a Car Mode to loop the video...