What Are These Things Called In Rochester and Where Can I Get One?

Just before last week's Blizzard Cyclone Bomb, I took this picture on Mary's Pond Road in Rochester. What are these things?

I talked about them this morning on the show, and Abby and Gazelle say that they keep your mailbox from getting buried in snow from the snow plow. Do they really work? What are these things called...and where can I find one?