San Francisco International Airport is increasing its efforts to advise travelers renting vehicles about the California law which requires “hands-free” operation of cell phones while driving, SFO spokesman Michael McCarron said.

On Monday, airport officials started placing advisory signs at all rental car counters as well as garage entrances where customers pick up rental vehicles. Passengers renting cars are also advised via the airport’s public address system, McCarron said.

SFO plans to mount permanent signs on the exit ramps of the garages and on the exit roadway of the Rental Car Center, reminding out-of-state drivers about the California law, McCarron said.

The state’s vehicle code prohibits drivers from using a handheld wireless telephone while operating a motor vehicle. Drivers 18 and older may use a “hands-free” device. Violators will be fined $20 for the first offense and $50 for each subsequent offense.

“We want to ensure that everyone renting a car at the airport’s Rental Car Center is well aware of California’s “hands-free” law and that everyone leaving SFO is in compliance,” said airport director John L. Martin.