Here's an update, if anyone's interested: Today, I spoke to the Dep't of Public Works, and got, "Sorry. Call a lawyer". This evening, I by chance met the offending neighbor's next door neighbor. This man told me that he witnessed the plow push the snow across the street and onto my property. He got the plow driver's name and phone number. He contacted the police on his own. What a saint! He said that the police told him that I needed to file a complaint with their dep't. So, I called the dep't. and they had no record of the complaint I already made, or of the officer coming out and speaking with me. Arrrgghh!

But, they send out the officer who had met with the good samaritan neighbor, and HE was sympathetic. He remembered "the 15 ft. pile" on my property from last winter. He gave a strong warning to the driver and my neighbor. This evening, I finally saw the plow driver and spoke to him, assertively, not abusively. I don't think he'll be shoving the snow onto my property again.