Harry, whose attention had been focused entirely on the two beside the window, saw his father: slight, black-haired like Snape, but with that indefinable air of having been well-cared-for, even adored, that Snape so conspicuously lacked.
Thinking a lot about this recently. How much it says about his family.
Because you can be frightfully poor - and still cared for. Still loved.
Contrast to Remus, who was also incredibly poor (he was an adult here, and likely did all this himself, but still):
The stranger was wearing an extremely shabby set of wizard's robes which had been darned in several places.
[...]
... there was a small, battered case held together with a large quantity of neatly knotted string. The name 'Professor R. J. Lupin' was stamped across one corner in peeling letters.
He is shabby. His clothes and things are threadbare and faded.
But they aren't unloved. The holes in his clothes are darned.
He hasn't fought with his case to keep it shut with string - he has carefully, neatly knotted every string. His name is stamped on it.
Severus isn't ever described with that level of care.
Like Harry, he is described as wearing clothes that aren't even his - for Harry it's Dudley's too-big hand-me-downs, for Snape its his (probably) fathers coat and mothers smocklike blouse. (DH, ch33)
Harry's guardians didn't care for him.
Through this parallel - neither did Severus'.
His grey, shabby, threadbare hand-me-downs weren't carefully darned, patched or taken in to fit his body. His name wasn't stitched into his collar or stamped on his bags - his things were not his.
Harry had his parents' love in the form of their money left behind, so he could start fresh with his own things, his own identity.
Severus did not have this love, either.
No matter the state of his robes, whether money had been scrounged to get him a set all his own, he carried his lack of care on his being.
...that indefinable air of having been well-cared-for, even adored, that Snape so conspicuously lacked.
It's a powerfully descriptive sentence.
As cute as the image of his mother giving a shit about him is - it's quite clear he was neglected by both parents, not just because of poverty. Poverty doesn't cause a lack of love.
His mother at least spoke to him about the Magical world, but she never imprinted 'being adored' into his heart, his being.
Even Tom had that love. His mother poured her love into him with her dying breath, named him and made sure he would be cared for.
He rejected that love - a powerful image, especially in this series.
An image Snape once again both defies and parallels.
He was not loved by his mother yet took pride in her, stamping his book with his self-chosen title and name based on her lineage - a little like Remus' stamping his bag with his new title and name, and a little like Tom picking a new identity.
Excuse this tangent: he gives me Morgott (Elden Ring) energy - who was basically scorned by his mother for being born with horns, literally thrown in the trash by her and her 'religion' - yet dedicated his life to them, doing what he thought was right, worshiping at the alter that scorned him, wearing their name with misplaced pride.
Meanwhile his twin brother, Mohg, shed his mother's name and found his own love. Made his own title. Started his own cult family, with blackjack, hookers and a LOT of blood. Lord of Blood, making his own alter to be worshiped at. Tom-like.
Uh yeah anyway - Severus wasn't loved and it's very sad, yet he dedicates his life to doing loving things even as a grumpy pants.