Following steps are accomplished
1.In Spark under Actions->Join conference room, click on the conference room "Conf"
2.Click on Configure room icon, it displays a pop up window: "Configure chat room" , Check on the check box : "Visitor" available for the option: "Roles for which presence is broadcast" and click on Update.
3.When you check the "Configure chat room" window again , only the Visitor check box will be available and if you want to change the option to Moderated or Particiapant, you cannot change it as there will be only Visitor option present.
Available options are: Participant, Visitor, Moderated. All of them should show on the Configure chat room dialog: checked or unchecked - but it seems that the ones that are not checked do not show at all, and the ones that are checked appear as an uchecked checkbox