Is anyone familiar with I facial expression where someone smiles for only a brief instant. They otherwise have a melancholy look on their face.

Maybe it's trying.

Trying… That’s an interesting thought. I had gathered as much that it might mean Goodwill despite not feeling good

Trying… That’s an interesting thought. I had gathered as much that it might mean Goodwill despite not feeling good. Sometimes I wish I had an x-ray mind to know what other people were meaning.

Me too! But it would probably ruin some pretty special moments....

This makes me think about Eeyore from Winnie the Pooh.

Haha :-)

There is an actress who always exhibited this phenomenon,
she was the star of 'Alice" one Linda Lavin.

It was freaky, her face would be unanimated, then suddenly
she would smile, then that would die in an instant and
she was plain-faced again.

Plain, smile, plain, smile..all in seconds.

I'm very familiar with it, and I know that it isn't connected to only ONE intent.

What it means, depends on the exact circumstances.

If you're in the midst of a conversation with someone, they are overall sad or bored, and they lock eyes with you for a moment and flash the quick smile, it CAN mean that they are trying to tell you not to worry about them. It can also mean they want to tell you that they just said the last thing they did, more as a wry joke, than as a direct serious statement. Or it can mean that they want you to know that they consider you to be "on their side."

Bottom line, even those of us who are NOT commonly plagued by difficulty "reading" expressions, have a hard time knowing what the "flash smile" means.

Overall, I think the main thing to try to recognize, is when the person knows you saw them smile, and when they think you didn't. If they know you saw it, as in they did make sure you were looking at them first, then its likely they were trying to tell you something with the smile. If they think you didn't see it, and they were looking at someone else as they did it, they may have been using it to talk ABOUT you, or about the overall situation, to that other person.

What they are looking at is the best way to make an educated guess.

I know from experience that people who do not often socialize by choice or otherwise do not change/show expression as much. The same can be true due to being in an environment where socialization might be seen as inappropriate -such as a workplace where there is hypersensitivity to harassment, etc.

I am very reclusive, and my expression could usually be described as "bovine" -like... cow standing in a field bored out of his gourd... even though my mind is thinking a million things.

If they are looking in your eyes at the time they smile, it is easier -usually means they like you -especially if they have a soft look in their eye -unless they are smirking and shaking their head a bit rather than smiling -which means they think you are a dork -which isn't necessarily bad because some people like dorks.

I get a lot of smirking head-shakers -and some confused puppy looks.

There are such things as micro-expressions (interesting study), but they can be confused with transitional expressions -where the face seems to be expressing something but it's really just between expressing actual thoughts.

"Sometimes a cigar is just a cigar.": Freud.

And a brief smile is just a brief smile, a moment of pleasure, or humor.

And what you are interpreting as a "melancholy look", could be just their normal resting face.

I looked it up. That is precisely what I described but means something different, haha. “Alice”, if I get the context right, smiles when engaging with one actor then stops when walking over to another. It is like the expression is a step in the direction of getting in the mood really quickly for a particular situation.

This woman I saw nonverbally indicated to me that she wanted me to see the flash change. I can’t lay a finger on it.

That actually makes no sense yet; her wanting me to not worry about her.

No one answer. Can be a brief moment of real pleasure, can be a fake smile just to please you, can be being polite when something doesn't really interest them, and so on.
Context, my dear Watson...

I see her often at the gym. She is very communicative and playful. She usually does not talk to me much, I am just around and she often get some sort of non-verbal expression to me at least once just as a friendly acceptance of me being there.

She is warm for sure, but no evidence of flirtatiousness. I am aware that there is no romantic potential with her, and she is married and has children. Nor would I want to cause all those problems associated with flirting with someone else’s lover. I just want to understand what she means. She was looking right at me. I was smiling and feeling more capable than usual. At the threshold entrance we were crossing paths at the gym, I was smiling more than usual and was looking at her inquisitively to see how she was doing, she looked right at me, and flash smile from a melancholy state. I just want to know what she means, hahahahaha.

Ooooooh loool! I paint a different situation in my head now!!!!

No, I definitely don’t think it means anything involving waiting in expectation for. This seemingly mundane detail is an element of communication. Communication is a wonderful thing. Even if I don’t know what something is, it is what it is.

I see said the blind man, to his deaf and dumb daughter, who picked up a wheel and spoke

It means she's thinking of getting into your trousers

You go straight to the funniest thing possible

I've never heard of this ' I, ' smile thing
But I've heard of macro expressions, and I assume ( probably wrongly ) that it's the same or similar

Weird thing is ( or maybe not so weird, I don't know ), they can be seized somehow

For instance ( this used to happen to me awhile ago, thankfully not anymore ), somebody might tell you, that their parent just died ( but your mind wanders to something amusing or pleasing ), and you smile. Obviously as soon as your conscious of it, you feel terrible about it, and rearrange your face. Works the other way too. We're going to get married ( cue visions of, I don't know, when your cat died ) . aaarrrggghhh wtf is wrong with me. That's great news I hope your both really, etc, etc

Anyway, she's definitely thinking of getting into your pants. Doesn't mean she wants to cheat on her husband or anything, but mine wanders... I wouldn't mind a bit of that , oops I've been caught

Or maybe she wants you to join in some devilish menage a trois that ends with you buried under the porch. Or she though of shoes

Honestly, who knows how their mind works ( one would have popped up here and berated me for being terrible for saying what I've said, regarding, smile, woman, pants. But now she won't , weird, huh )