When a user is logged out, there are some elements that they can interact with:
And this is how they behave:
- Upvote/downvote: show a "join the community" pop-up with the required reputation.
- Bookmark (only on the question): show a tooltip, informing the user to log in or register.
- Timeline: the same as logged-in users.
- Share link: the same as logged-in users.
- "Improve this question/answer" link: the same as users without full edit privilege, except without "you are not logged in" text.
- Follow: show a "join the community" pop-up.
Personally, I would expect the "follow" link to behave like the "bookmark" button since both do not require any reputation. Though, whether the tooltip or the pop-up is more preferred, can we have it more consistent?