Today, I Am a Lawbreaker: A Freakonomics Contest

Yesterday, and for much of the past year, I regularly did something that was perfectly legal.
Starting today, if I do the same thing, I am breaking a New York State law.
What is it that I’m doing?
The first correct answer earns a signed copy of SuperFreakonomics or a piece of Freakonomics schwag.
Addendum: The answer and winner are announced here.