Another 2¢ worth:

I don't want to banish announcements to a ghetto. I like McGrath of Harlow's suggestion of a tag to allow them to be filtered, and I like Barbara's ANN (Announce) prefix very much. I think it sounds more pleasant and useful than EPH (Ephemera), TEMP (Temporary), P&E (People and Events), CUR (Current), or any other label I could think up.