Good Question!! I have been wondering this for some time myself. My car does not have one on it. Theres a guy around the corner from me w/ an 84 GN that doesn't have one. Herb's car did have one and I have pictures of a 16k or so 84 GN that has it on it. So I don't know what to believe!
And the 3.8L Turbo emblems were only on the non-GN's, that is common.