Will return 1 if the player is a raid officer or 0 if the player is not. (As of 2.4.3 seems to return nil if player is not raid officer)
if (IsRaidOfficer()) DEFAULT_CHAT_FRAME:AddMessage ("I am a raid officer."); elseif not (IsRaidOfficer()) DEFAULT_CHAT_FRAME:AddMessage ("I am not a raid officer."); end
Confirmed: this actually returns true if you have the Assistant rank.
Edit 3.3: May 27th 2010. It appears that IsRaidOfficer breaks any macro it is used in if the user is not a raid officer. It's been confirmed by others in my guild, but I'm not sure of the exact specifics. More should probably be done to determine whether or not it breaks based on that.