No pets in lease, saw cat in window while driving by property

[Coco Zuniga]

K, so I know these are the kinds of things I signed up for when I became a landlord, but man, I'm not a happy camper...I drove by my property and saw a cat in the window of the house. My lease has a strict no pet policy and the renters were very aware of this.  What is my next move?  :(