FYI the DOJ/FBI does not utilize Lincoln Town Cars or Escalades for ops. You'll want to keep an eye out for Chevy Impala, Ford Crown Victoria, Chevy Suburban, and in rarer cases Dodge Charger (no spoiler) and GMC Denali. Typically they're darker colors, but the easiest indicator is a massive amount of tint on all windows. Remember, official vehicles will have the default state license plates without any sort of bumper stickers or license plate holders. In Maryland, unmarked LE vehicles typically use an older license plate instead of the newer design.