does "unmarked"mean "without alarm whistle?" or anything else?
Even Liz realized that there would be no speech now. It occurred to her that Johnson might have gone to a hotel, and entering an airline office she borrowed a phone to reach him that way. Marie, more realistic, poured out their story to a sympathetic Dallas policeman. He put them in a state police cruiser, and they careened back to Parkland, pleading with the driver all the way to slow down. Drawing up, they saw Lady Bird in the second unmarked car. She, too, had just made it; after leaving Nellie she had flown downstairs and was trying to catch her breath. With a fluttering hand she signaled them to come along, and they squeezed into the hastily assembled caravan.