flash warning 

Flashing your vehicle lights to warn other drivers of upcoming police speed traps.

A nice gesture so that other drivers don't have to pay speeding fines.

A reminder for people to slow down while driving.

Note: If ya get the signal just smile and wave back :)

Good thing that guy gave me the flash warning otherwise I would have been out $150.

flash warning by good samaritan helping out December 30, 2008

flash warning 

a term used on social media for posts that contain flashing lights or flashing pictures and is used as a warning for people who can't handle it or who have mental illnesses because it could trigger seizures for them etc..

*sees a post*

the caption reads : flash warning!!
*quickly clicks off*
you : oh thank god i could have had a seizure

flash warning by Lana Del Rey is god1 April 26, 2021