Safe Winter Sidewalks

Annoyed every time you almost break your neck on your way to the train? Just received this information in my inbox:

It's easy to curse your neighbors when it takes you ten extra minutes to get to the C in the morning because you have to wade through snow or jump over slush. We're making it easy for people to do something constructive and neighborly about keeping their block shoveled this winter. We'll send you cards, and all you have to do is drop them in the mailbox of your neighbors who shovel. A little positive reinforcement goes a long way towards making a snow-free and friendlier block. This definitely won't work for people living in larger buildings controlled by a management company, like in downtown Brooklyn, but in mid- and low-rise areas with more homeowners, like much of Clinton Hill, it's a good solution to the eternal neighborhood problem of sidewalks blocked by snow.

What do you think? Would these cards work?