Takedown your first cop.
Easy to do.
Cops are the blue arrows that you can sometimes see on your mini map.
You can find them everywhere in the city. They also appear frequently during a race and at every time during a race against a "most wanted car".
When you saw a cop, just try to hit him anywhere, the IA is a little bit stupid, they will crash at almost every try.
If you fail at the pursuit and get busted you will earn another trophy: