Well, alright. I thought about it.
I know a few ENFJs and INFJs.. and maybe they have something in common facial expression wise.. (They've taken the test themselves and have either mentioned it to me or posted it online.)
They use Fe.. but their gazes are not really soft usually. They are more evaluating, it is like they are trying to get a read on you. One of them is a manager at my work, at first she made me uncomfortable and I couldn't understand why.. a few other co workers have mentioned this, too. We decided it's because she seems to always be trying to glean unspoken info from us.
I also had an ENFJ room mate like that, once. As if they are listening to your verbal communication, but focusing more on the non verbal.
I know two INFJs.. one a male, one a female. Same thing. Evaluating, though not unkind. I'd describe it as more of a perceptive secret comprehending gaze.
But I am not sure if that speaks to all Fe users.. just a few I know. I wouldn't be able to pick an ENFJ or INFJ out of a room of strangers based on this info, though. Maybe I'm not that perceptive..
We're a little off topic, but it's interesting.