I think someone mentioned earlier, or on the other thread, that unless otherwise noted that all rights are reserved to the copyright owner (the creator). So you don't have to take any special action for it to fall under legal protection (meaning something actionable in court). And indeed I would suggest that publishing works or sharing them is one of protecting them because all these places use time stamps, and are third party, and so I would assume are valid evidence as to ownership (as well as having all the creation files if you have a big enough hard drive to save that stuff).