Grab a gallon of ordinary laquer thinner from the hardware store. Put some in a small bucket or pan and use a wash cloth soaked in it to scrub away the paint. So long as it hasn't baked in the sun for a few weeks that should soften the paint and wash it away. Rinse the rag in your bucket frequently. When you get down to the last residue, pour clean thinner on the area and wipe down with a clean rag only dampened with the thinner.
If this doesn't cut it, your last hope will be Easy-Off oven cleaner. Get several cans of the plain old ordinary kind. Spray it on the paint and allow it to sit 5 minutes or so. Use dry, blue paper shop towels to scrub away the cleaner and paint. Repeat as necessary. I did this about 10-12 times on a gang tag that was a year or two old. It came off. Newly applied rattle paint should be much easier.
This will, of course, take off any wax on the car. Try to limit how much cleaner and rubbing you put on the car paint. Watch for your base color on the towels. That tells you you're working on the wrong paint. It should only be a problem if your finish is badly oxidized or your clear coat is missing or damaged.
Last advice, Go slow, be patient, work small areas.
