Given the potential for abuse, the insurance company probably can't really do much aside from writing a letter to the driver saying someone observed them drivin

Given the potential for abuse, the insurance company probably can't really do much aside from writing a letter to the driver saying someone observed them driving dangerously. Probably the letter should be more specific, include pictures, and it should not be entirely anonymous. You should be able to find out if someone is trying to make trouble for you. It might not even be legally possible anyway. Insurance companies have a lot of regulation.