* Creating or modifying a wiki page now generates a #wikiI'm concerned about the name space collision with user-generated and used hashtags of the same names. This wasn't a big problem with the calendar events as those tags have a distinct form that's unlikely to be used for ordinary message postings.
Granted GMF and Group_Help are unusual cases, but those three nouns seem way too likely to collide with something a member might use. GMF has that problem with #wiki already, and has near misses with the other two (#files and #photos).
Given that these new ones aren't intended to be used by members, I don't think it would be a bad thing to make them hyphenated also, as in
#file-notice, #photo-notice, and #wiki-notice or something of the sort. Not quite the same semantics as #cal-notice, but close enough.