I've never seen that interpretation, but I have to say -- as someone who is not a fan of the /s, I find the fact that it could be interpreted as the exact opposite of the standard meaning pretty funny. In fact I think I will start using it this way, to sow discord among the /s fans. /s

As the "end of sarcasm" marker, it means both:

"{sarcasm here} /s {seriousness here}"

We need an emotional tone markup language. ETML.