A McDonald's in the Netherlands has a sign by the door that reads: "You steal, you're marked." And by marked, they mean covered in a synthetic DNA spray.
If it deploys as a mist how do they keep it from getting on innocent by-standers? I imagine the stuff is near impossible to remove, so are the innocent bystanders marked for months? Years?
Businesses and banks here use a purple or blue dye that is clear until activated by touch or the spray. Doesn't wash off easily and can be spotted by anyone.