
Be careful that you do not have any weight of the helmet resting on the
mirror.  It will depress the foam liner in the helmet.  That is not the
kind of foam that bounces back, like foam rubber.  Its purpose in life
is to absorb energy in an impact as it is compressed by your noggin.
If your mirror compresses it, there is that much less energy absorbing
capacity left to cushon your noggin in a crash.

I found the right handlebar to be a good spot, if on the sidestand.
Hang with the chinbar facing up, balanced across the grip and brake
lever such that the weight of the helmet doesn't compress any of the
chinbar foam.  This is more challanging with an open face helmet.
