A spike in auto theft has Minneapolis police turning to billboards to remind drivers to keep their keys with them.

“You Hold the Key to Preventing Auto Theft,” read the signs that have appeared across the city.

The message is simple: Don’t leave keys in an unattended car.

More than 530 vehicles have been swiped in the first six weeks of the year, or an average of 12 vehicles a day, the Minneapolis Police Department said. And most thefts were preventable, it added.

“These were thefts with the keys in the ignition and the vehicle running with no one present,” a police department news release said.

Last month, police department spokesman John Elder said 73% of cars stolen in January had been running and left unattended.

Stolen vehicles often are used in other crimes, he said.

The police department and the Downtown Improvement District teamed with Clear Channel Outdoors to carry out the campaign.