What is a 'Prohibited Person'?

Ciaron O'Reilly very kindly spoke at a political session I hosted in 2013 on Bradley/Chelsea Manning

Ciaron O'Reilly, a non-violent Catholic pacifist has been arrested in Brisbane, Australia, where the G20 is taking place. The offence against Ciaron? It is for being a 'prohibited person'. What on earth does a 'prohibited person' mean? Some things just stop you in your tracks and this one did it for me. I have only ever seen the word 'prohibited' being used at the airport or certain public places where people are prohibited from carrying dangerous things such as sharp metal objects or glass. See example below. But what does a 'prohibited person' do or not do to become prohibited?

A quick Google search throws up this term in connection with firearms. Ciaron was not carrying firearms. A non-violent Pacifist would not be carrying arms now would he? It turns out that even Ciaron does not know what he is being charged with in connection with his arrest but it would not be far off the mark to guess that it is because he wanted to confront Barack Obama over Julian Assange and Chelsea Manning. America being America cannot tolerate any dissent over who it calls a 'traitor'. While I don't like Julian Assange myself I see no reason why someone like Ciaron cannot be free to heckle Obama. Isn't America meant to be a great Democracy? Chelsea, formerly Bradley, Manning alerted the world to some truly horrific atrocities being committed by their soldiers in Iraq.  Yet, it is him who is in prison while those soldiers are free.

Democracy is increasingly becoming an ideological thought that only seems to exist in people's heads and recedes further and further away from the reality of this world which is being overtaken by heavy handed behaviour.  Free Ciaron O'Reilly.