Sometimes, you have no choice.
AOAA requires the permit to be affixed to the left side of your helmet.
MRA requires it be visible when followed (the back of the helmet typically works), but there is no requirement for a specific location.
RAC just requires that the permit be visible on the rider and gives you a nice holder with a large pin (much like a hunting permit holder).
USFS for the ANF requires the permit be attached to the arc of the cables infront of the rider and unfurled like a flag. They recommend that the permit be "rolled up" when transporting the bike from location to location. Mutilated permits (from wind damage) are not considered valid and must be replaced at the rider's expense.
Years ago, the ANF had no such requirement and attaching the permit to the side plates was sufficient.