Question:  How do I tell if a traffic signal controller is equipped with a GPS or satellite clock?
Answer:  The first clue is shown in the photo below.  There should be an antenna on the top of the cabinet, often referred to as a puck because of its shape.  

Inside the cabinet the unit is typically mounted in the back, near the top of the rack, as shown in the photo.  In this case it is a McCain clock unit.  

The black cable connects to the antennae.  The grey cable connects to the controller unit via the C2S (communications)  port.