Is it possible to license one's online posts?

I would be interested in licensing all of my posts, and comments (or any other applicable user-created content) under CC BY-SA 4.0. Is this legally feesible? How would one go about this properly? Is it enough to just state in a bio something like "All of this users posts are licensed under CC BY-SA 4.0", or would I also have to add "This work is licensed under CC BY-SA 4.0" to the end of every post, and comment that I make?