Count me in too, I also don't see the need for the reg numbers, normally with a petition you need an address, phone number or e-mail so authenticity can be verified. I also don't see why the petition has to just be BMW owners as prospective owners may also wish to register their concern.
I also wonder if there may be a sale of goods act case here? Is the car security 'fit for purpose'? I guess this would take some sort of 'class action' but could certainly lead to BMW taking notice.
Finally - is it worth contacting Thatcham? If it is them who have signed the car's security system off as 'Class 1' are they not accountable?