Yes emdashes are very much a sign. I stand by this. Why?
What is the key combo to make an emdash?
On a phone keyboard, sure, it's as hard as an accent sign (á, for example), difficult but not twrrible. But on a keyboard? Yeah, no one is typing in Alt combos when literally any other construction will do.
> On a phone keyboard, sure, it's as hard as an accent sign (á, for example), difficult but not twrrible. But on a keyboard? Yeah, no one is typing in Alt combos when literally any other construction will do.
For me, --- gets converted to an em-dash (—) while typing, if I have my input method (ELatin) enabled. I'm so used to typing in while working in LaTeX I can easily slip it in elsewhere.
Right control (compose), -, -, -. Alt combos are for Windows users who haven't discovered WinCompose, everybody else has some built-in way to enable it in their OS. If they're not on a US-English keyboard, either compose or AltGr is likely already enabled.
Yes, it's very tell tale in forum posts, but blog posts are often rendered markdown, where it's easy to type `--`. But it's not conclusive evidence in either case! The false positive rate is still not negligible if you only go by em dashes.
On macOS (and iPadOS if used with certain external keyboards), it has long been `Option` + `Shift` + `-`. Desktop publishing folks memorized this, and other, typographically helpful key combos many years ago.
