The Riot Act is still used in
Canada today; it was recently read during the anti-
FTAA protests in
Quebec City.
The text of the act is approximately as follows:
"Her Majesty the Queen charges and commands all persons assembled to immediately disperse themselves and to peacefully depart to their habitations or their lawful business. God Save the Queen."
The Riot Act does not have to actually be heard by any of those "rioting". No attempt need be made to broadcast it via PA system or megaphone. A symbolic attempt is all that is necessary. For example, the magistrate can stand at an open window near the "riot" zone and read the act. It is thereafter in effect.
Theoretically the Riot Act allows "rioters" one hour to disperse before an increase in the level of police response.
In Canada the Riot Act allows police to arrest people on sight, which is usually not allowed as Canadian police, by law, must immediately charge you with an offense (unlike U.S. police).
The reading of the Riot Act is not a declaration of Martial Law.