I've been looking a place to put my helmet when parked. Looked at different helmet locks but wanted something more stealthy when not in use. I know some aren't concerned with this and that's all good.
This is what I came up with. It's two D rings and a vinyl coated clamp bolted with the saddle bag bolt.
Just thread the strap through the D rings, close and lock the lid. I've used this for a year with no damage to the weather stripping.
Yes the strap could be cut but would like to think someone that's going to steal a helmet does want to bother getting the strap fixed. A cable tether strap with a carabiner to the D ring could be used for more security or if the helmet strap isn't long enough.
In the end if someone wants it, they're going to take it no matter what.