It is first seen in "Scary-oke" when Agents Trigger and Powers arrive in Gravity Falls, and Soos asks Stan what the secret code is if he sees a government vehicle near the Mystery Shack.
In "A Tale of Two Stans" it is seen when Agent Trigger and Agent Powers leave, after having their minds wiped and dismissed by Ford.
The car is black, and has a license plate with "USEXEMPT" on it. The words "U.S. Government" are written on the side in white letters, with the symbol of the agency Trigger and Powers work for below it. It also has a sticker saying "Honk if you want to be arrested" on its rear bumper.