A speed screen expert will also be observant of the leading car's braking habits. If he/she randomly hits their brakes, it's likely that they've spotted an officer up the road. Their brake lights act as a potential police warning system.
The ideal speed screen is one in which you are sandwiched between two speeding cars, one in front, one in back. The rear car will screen you from flanking police cruisers.
Wife: Can you drive faster, we're late.
Husband: I don't want to get a ticket.
Wife: Just use a speed screen you pussy.
Driver: Dude, this guy coming up behind me is flying.
Passenger: That's a perfect speed screen, get behind him and step on it.