well, even the windshield is illegal to touch technically. Banners are not truly legal.
http://www.tintlaws.com/
http://www.tintcenter.com/laws/NJ/
http://www.solamatrix.com/documents/State%20Law%20Chart%207-07.pdf
rear door windows and back windows are fair game as well as any 1/4 windows behind the driver(as on some 2 dr cars)