plastic razor blades dont work too great, and hairdryer has never worked for me. If you have access to one, a pressure washer. A pressure washer will rip that sucker right off real quick. Just be carefull not to get too close to your paint and stay away from chipped paint. If you don't have access to one, use a regular razor blade, but use this with extreme caution. It of course helps to have detailing experience. If you don't want to do any of those then just use your fingernail, then use some 3m tar remover or equivalent and lots of elbow grease. Takes a while but worth it in the end.