There is no AF-S for Sigma. AF-S is a Nikon strictly Nikon mount spec. It not just referring to Nikon's motor, but also the entire electronics spec for Nikon Lens. The wave motor in Nikon is referred to as SWM = Silent Wave Motor.
Nikon AF-S and Sigma HSM are NOT relatively the same, especially here we are talking about Canon EOS mount. Want to say something, say it accurately. If cannot, might as well don't say anything.