[Iconic944ss]

Searched for ages for the legal stand point.....from memory for a bike it used to be "forward of the rider, now higher than (cant remember, 4 foot?) and visible from the road side"

Interestingly the DVLA website only says...

"A vehicle licence (commonly known as the tax disc) shows that you have paid the necessary vehicle excise duty [VED] for your vehicle. It shows the registration mark (number) and the date up to which you have paid VED. You must display this disc on the left-hand side of the vehicle's windscreen. If the vehicle does not have a windscreen fitted, you will need to display the disc on the nearside of the vehicle (the passenger side)."

I agree with Derek though - mounting anything else on the front wheel / forks needs careful consideration.