When choosing wording for software or websites, it is worth thinking about the phrasing of opposites. If you log in, then you should log out, not log off. If you subscribe, then you should unsubscribe, not cancel subscription. Buttons should be yes and no, not yes and cancel.

If it doesn't work, e.g. sign up, then consider a different phrase, such as register, which does.
12 September 2007