On the mission Siena, you will have to chase a traitor across rooftops. There will be seven satellite dishes scattered throughout the chase on rooftops next to the one you have to run across. The satellites are white and you can see them sticking up on the rooftops. When you shoot each one they will fall over and you can move on to the next one. If you shoot one and die before you reach the next checkpoint, make sure you go back and shoot it again for it to count.
For a complete guide on where exactly the seven satellites are, you can use THIS walkthrough by Frankie B1.