one of the documented procedures in this installation of the ACS
What it does:
Pages that are consider whether to display a user's name or email address should test to make sure that a user's priv_ from the database is less than or equal to what ad_privacy_threshold returns.
Defined in: /web/philip/packages/acs-core/security-procs.tcl

Source code:

    set session_user_id [ad_get_user_id]
    if {$session_user_id == 0} {
	# viewer of this page isn't logged in, only show stuff 
	# that is extremely unprivate
	set privacy_threshold 0
    } else {
	set privacy_threshold 5
    return $privacy_threshold