I'd spell USE YOUR TURN SIGNALS.
Roadwriting: Guy Turns His Truck Into A Dot-Matrix Printer That Writers With Water

Not unlike the skywriting planes that use a similar technique to create strips of letters, maker of things Ryder Damen went and modded his truck to spray jets of water to print letters on the ground as he drives around like a giant dot-matrix printer. That’s cool. I want mine to spell EAT MY RUBBER. But instead of water it’ll be spelled in gasoline AND LIT ON FIRE. Hoho *rubbing hands together excitedly* I know what I’m doing this weekend! “Low speed chase, getting arrested again.” There’s no question.

Thanks to my dad, who agrees anything to prevent idiots from tailgating.