Good catch! That's quite interesting about the head nods Ralph!
Of course, people might argue that it meant that Fritz and McMillon were indicating that all was well and ready to go. That would be the obvious argument.
However, what they don't realize is that all was NOT well and they weren't ready to go - not in terms of the supposed safety precautions they had planned out, anyway.
First of all, the plan was that Oswald was supposed be put in Fritz's car which was supposed to have already been backed up in the driveway and next to the end of the hallway, but Dhority had not yet begun to back the car in. That didn't begun until after Fritz reached the edge of driveway himself, and the car didn't stop until after the shooting had already occurred. Secondly, all news men were supposed to be next to the railing, not part of the pitiful line of protection and security that was in place. Pappas and Pettit were in the middle of the driveway in between actual officers, intended for security. Fritz and Mcmillon would have seen this, of course.
Obviously the head nods by Fritz and McMiller were indications that the real set up was in place - when Oswald gets pretend shot by a pretend Jack Ruby. There is no doubt that Detectives in charge of an actual secure transfer of their prisoner would have instantly seen that the car had not yet been moved and that several reporters were not behind the "guards".