The phrase 'It's on' signals that a plan, event, or contest is confirmed and happening. It often marks the start of a challenge or conflict, like saying 'game on'.
My advice to you is not to inquire why or whither, but just enjoy your ice cream while it's on your plate. Thornton Wilder
In Paris, one is always reminded of being a foreigner. If you park your car wrong, it is not the fact that it's on the sidewalk that matters, but the fact that you speak with an accent. Roman Polański
The majority of people perform well in a crisis and when the spotlight is on them; it's on the Sunday afternoons of this life, when nobody is looking, that the spirit falters. Alan Bennett
We need to talk. All of us. About what we're going to do now." "I was going to watch Project Runway. It's on next. Cassandra Clare
Let freedom ring, unless it's on vibrate. Joss Whedon
Much has been written about Generation X and the films about it. Clerks is so utterly authentic that its heroes have never heard of their generation. When they think of "X," it's on the way to the video store. Roger Ebert