A more thorough explanation:

A copyright notice is a statement that a work is protected by copyright law. It is usually included in each published copy of the work and takes the form of © (year of publication) (name of basic copyright owner). Although a copyright notice is not required for a copyright to be valid since March 1, 1989, it still provides certain procedural advantages. The phrase “all rights reserved” is no longer required.

Example 1: A book published in 2021 has a copyright notice that reads © 2021 John Doe.

Example 2: A website has a copyright notice at the bottom of each page that reads © 2021 Jane Smith.

These examples illustrate how a copyright notice is used to indicate that a work is protected by copyright law and who the basic copyright owner is. It is important to include a copyright notice to provide certain legal protections and to inform others that the work is not in the public domain.