Mate,
Indeed, the "Sigma 18-200 f3.5-6.3 OS" is Sigma's official designation for this lens, only for the Nikon mount that is known as the "Sigma 18-200 f3.5-6.3 OS/HSM", thus there's a reason why an "/" sign is used instead.
From Sigma's website, if you observed on this page:
http://www.sigma-photo.co.jp/english/lens/digital/18_200_35_63_os.htm
Look under the left boxes, and look for the corresponding mount, you'll see as such:
Corresponding AF Mounts
SIGMA,
CANON [18-200mm F3.5-6.3 DC OS]
NIKON (D) [18-200mm F3.5-6.3 DC OS HSM]
The Canon mount only comes with Micro motor for AF drive. As in my earlier post, I have played with it before, it is still quite fast in AF, but comes with some noise.
If comparing with the latest Canon EF-S 18-200 f3.5-5.6 IS, also does not comes with USM motor drive, if that is any consolation.
Good luck in your search for a suitable lens.