The SIG leaders list is a list for SIG leaders and ACM officers to coordinate on make private announcements or ask SIG related questions. The admin interface is visible from the mailman page, acm.cs.uic.edu/listserv, and people cannot add themselves to the list. From the admin interface add the new leaders and officers and remove old ones if and only if they are no longer going to advice new leaders on running SIGs.
The ACM annouce list moderates new members by default so prevent unauthorized postings. The current ACM officers will need to be added as moderators. As well, any new SIG leaders or event planners will need the ability to post to the list unmodded. The announce list forwards all emails to the main list as well so ALL official announcements should go through it. Giving then the ability to post can happen one of 2 ways.