stained car hood

Recently my car was vandalized and someone sprayed some substance on the hood of my car. when I found it next morning it had probably been sitting all night. The substance was foamy with no smell and left a yellowish stain of what they wrote on the hood.

I have only tried soap and water to get out the stains but it doesn't appear to be working. They also appear to have sprayed a little on my wifes car but it only on her tail lights. With a little elbow grease I was able to get most of it off her car. Any ideas on what I can try to possibly get these stains out with out damaging my finish. I sure hope I don't have to get the whole car painted. By the way the car is a White 1999 Honda Civic LX.