Hi, we have not a cancellation form, your subscriber can write to you to check if they’re subscribed (never happened to me in 10 years…) and you can add an unsubscription url even on welcome email so they can keep those message to unsubscribe.
But, just an opinion: if someone subscribes the only reason to cancel is when you send him a newsletter (which has the cancellation link)… hence I won’t worry too much to have an unsubscription form on your site.
Stefano.