Dr. Max Hudson: If I start to go crazy can you... take care of me?.. In the back of the head.
Diana Skouris: You won't even see it coming... Dr. Hudson?
Dr. Max Hudson: I just gave you permission to blow my head off. You can call me Max.
In episode 17 there are some scenes showing sick 4400s all around the world. One of them is being carried into an ambulance car in Frankfurt, Germany. The ambulance car's number plate begins with the letters FM meaning Frankfurt am Main. The correct abbreviation for Frankfurt am Main on German number plates is F - not FM.