Siren:
Set the rear spoiler to type 5 for the 
R30 and R30M, then use the horn. 


Green Rabitt:
When in the garage, choose the sticker 
that resembles a jester/joker. It is 
black and white with a line down the 
middle separating the colors. Put it on
your car then hit start. When racing, 
go to first person view and you will see
a little green rabbit looking thing 
hanging from the roof of the car.