I don't notice which hand they use, but more often than not, lefties will write with their hand curved over (and smudging) the text they just wrote instead of from beneath (and not smudging.) That's when I notice. So when I notice, I don't say, "You know you could prevent getting graphite (or ink) everywhere..." I say, "Ah. Leftie."
I have seen righties do the same weird smudging with the arced wrist. Why do people write like that?
Because people learn how to write as young children in a place that typically has no experience with a proper technique for left-handed people, and re-learning how to write is not as easy as thinking to yourself that a different way would be better.
It’s probably good you don’t say the “you know” because that would be dumb as fuck.
We have a work area with school desks for some reason, of the crappy right-handed variety. So I notice when colleagues awkwardly try to use the desks and they're left-hand dominant.
I have a friend who is left-handed and insists on shaking hands left-handed. She will stare down anyone until they offer their left hand or do a weird fingertip shake with their right. Anyone who manages to shake her left hand without looking like a goober, she excitedly welcomes to the left handed club.
Only people I know because I like knowing who's left handed among my friends and family because it helps with things, seating areangements being one obvious example. Or so I don't just hand them scissors they can't use or something.
My wife and one of my kids is a lefty. I've kinda grown used to half looking out for it in others but only idly. It was fun watching each of the kids to see if any of them would be.
A friend of mine dropped an absolute bomb one day that I'll never forget: "There's only right handed and wrong handed". Definitely more than 20 years ago now but I never forgot it because I laughed so hard.