privacy messaging and private/public flag on sketches

I love that there's a publicly-visible list of sketches for particular users! But it's not necessarily intuitive for new users that any work they do in the web editor will be public by default. So there should be messaging that tells users that sketches they save might be visible to anyone.

Alternatively/additionally, it would be great to have a public/private (or draft/published, or whatever language you want to use) flag on sketches that determines whether the sketch appears in the user's list of sketches in the public view.

Of course this ticket runs the risk of spiraling out into a full-blown sketch authorization thing, and it's probably worth addressing at some point (if this hasn't already been addressed) things like making sketches that are only visible to the owner of the sketch, or to a group of users specified by the owner, or only visible to authenticated users, etc etc etc. But a public/private flag is the bare minimum necessary in my opinion!