According to this article that Creeper Joe posted a few days ago...

http://www.jrn.com/ktnv/news/SLS-Las-Vegas-employees-are-gearing-up-for-opening-day-271282581.html

"SLS actually stands for style, luxury, service. That was what it was originally meant to stand for," explains Herndon. "Over time, it shifted. Sometimes it's sexy little secrets or sweet little soirees. And it's just meant to be whatever the guests wants it to. But originally it stood for style, luxury, service."