Why “850” on a Ferrari 599?

Tonight I followed a stunning (and not red!) Ferrari 599 through Parnell tonight, oh the sound as it went up Parnell Rise!, but one thing had me wondering…
What is significant about the personalised number plate:850
Not Horsepower*, maybe $x1000?

* In spite of using the only sensible measurement system – metric – Italian cars often quote Horsepower in their model names. For instance my Bravo 155 HGT has an output of 113Kw, about 155 Hp