In spoken word, sarcasm in even the cleanest context always has the benefit of delivery paving the way for virtually guaranteed reception. A written indication does look silly when reception succeeds without its help, but guaranteed parity with speech seems like the winning maneuver.
The whole point of sarcasm is to say something you don't mean, and people who know you or other facts well enough, can get a dopamine hit for being able to infer that. It's just an ingroup/bonding thing and carries no information or value outside of that. At any rate, adding a /s is like saying "just being sarcastic", might as well not be sarcastic in the first place.
I think what you're describing is a subset of sarcasm, or potentially a separate thing that often utilizes sarcasm (significant overlap). A friend of mine will often suffix such statements in speech with "if you know you know" in the event that the delivery alone isn't sufficient to trigger everyone's memory, and "IYKYK" in text.
Pure sarcasm has no such prerequisite, which means that delivery alone (tone, cadence, and smirk) is almost always sufficient. These give away the fact that sarcasm is happening to roughly the same extent that "/s" does, just that we have more experience with the former so the latter tends to feel too spoon-fed.
Poe’s Law is vastly over-invoked. In any social setting where some amount of context can be assumed, it doesn’t apply.
And even if someone wanted to challenge me on that, I’d argue that the tiny number of people who would think “HN is a tech support site” is being said seriously aren’t worth the two seconds it takes to type “/s”.
The time it takes to type `/s` is a decent bit lower than two seconds, and yet the amount of time you've spend trying to argue that it's not worth it is vastly more.
I invoked Poe’s law sarcastically. I’m surprised you didn’t realize that, given how over-invoked it is here. I guess there’s always someone who doesn’t get the joke. /s. <—- shouldn’t be necessary, but is, obviously. /s <—- not sure if necessary here.
But this is exactly what I’m saying: if you’re sarcastic and the audience gets it, it’s good sarcasm. If you’re sarcastic and the audience doesn’t get it, it’s bad sarcasm. If you don’t have a clear enough context, just don’t be sarcastic.
There’s always someone who doesn’t get the joke. Even today, there are people who, at least at first, are fooled into thinking that Jonathan Swift’s “A Modest Proposal” was a serious proposal.