[aerohead]

If you just wanted to see your wake,fireplace ashes make an extremely fine airborne dipersant.I made 'play' landmine explosions with them as a young warrior,and they rival Hollywood's best effects.
Sprinkled on a dirt road,a photo-strobe can freeze a wake's image on film or digital camera as a car passes over after dark,vacuuming these minute particles up into the low pressure turbulence.
Caliche roads will do the same if you have access.
Also,if the car has been recently washed,the fine particles will leave an ashen- white patina of dust which will clearly reveal your car's separation line.
Neighbors will NOT understand and will likely be on their smart phone to the Sheriff's Department.
There are also edible powders which make a fine dust.They won't be any better understood.
Friends and family with private property 'acreage' make handy co-conspirators.