When this law took effect in 1978 it required that your copyright notice be on the piece in order to be protected and that stipulation remained until March 1, 1989 when that part of the law was amended to say the notice was no longer needed for protection. However, to avoid confusion it is recommended that you still include a copyright notice on each piece of writing. If the copyright notice is on the piece, there is no chance someone would assume it was in public domain and feel free to use it without permission.
The copyright notice needs to be prepared to fit an established format of three parts. That would include the copyright symbol ©, the word Copyright, or the abbreviation Copr.; the year of first publication or creation; and the author’s name. You may put the copyright notice on unpublished as well as published works.