The man in the camouflage on the right is wearing noise-canceling earphones.
He's also filming.
So the hand signal establishes a chain of custody for the evidence.
The feds can say, "Here's Agent Smith giving the prearranged signal that Antifa is following through on its threat against Andy Ngo."
Lawyers for Portland won't be able to argue that this person is not Andy Ngo.
I know that the man in camouflage is filming, because another man has linked arms with him.
This allows the man filming to concentrate on his job without worrying that someone will come up and bash him in the head.
The other guy is guarding him.
You see this kind of physical contact in SWAT teams.
@ThomasWic Note the guy with arms linked with the filming agent is giving a response signal to the guy in the foreground
Those who label words as violence do so with the sole purpose of justifying violence against words.