That was at one point in time part of the spec for "Photo Book" from Sloan. They thought they would need people to "sign" a release before they uploaded thier photos and info.
I believe the lawyers told them it wasn't required and thus it was never built.
Some interesting requirements came out of the discussion. For instance it maybe important for legal reasons to record the IP address and current password of the user at the moment they click.
It would be smart to implement it so it could be applied to a whole site, a subsite, or to specific programmer specified funcitonality within a package. (e.g. you don't need to "sign" to view data on but you do need to to upload your own data).