Apparently there are many secret cables buried in and around Washington, DC. The “call before you dig” guys don’t know about them, so if you dig one up, guys in suits driving black SUVs arrive. Which of course creates a social engineering attack:

So if I want to stop a construction project in the DC area, all I need to do is drive up in a black SUV, wear a suit and sunglasses, and refuse to identify myself.

Secret Government Communications Cables Buried Around Washington, DC