In all incarnations of Street Fighter II that I can recall, it is always shown as Street Fighter II'. Why? Somebody really needs to go to Japan and teach them English.
It's not all incarnations of Street Fighter II. The only games to use the "dash" are
Street Fighter II' (more popularly known in the US as "Champion Edition") and
Street Fighter II': Hyper Fighting (a.k.a. Turbo). The other titles in the series just contain "Street Fighter II", without the apostrophe.
I can't come up with a specific example off the top of my head, but IIRC I've seen the "dash" before in other Japanese titles. [Edit: one does come to mind now -- Street Fighter Zero 2', the home port of Street Fighter Zero 2 Alpha with a few changes
]
As for why the apostrophe is called a "dash" by Japanese people -- who knows.