"/s" means the person is being sarcastic, but there's also a name for this kind of thing: tone indicators. There are several tone indicators out there, all are meant to carry the meaning of the text. If I'm being honest, some tone indicators don't need to exist because they reintroduce confusion for people that need them for the full context.
tone indicators, you can Google them as there are a bunch. Do keep in mind tho: different communities sometimes user different sets of tone indicators /g