A copyright notice should be applied to a work to put others on legal notice that the work is subject to copyright.
A proper copyright notice includes the copyright symbol ©, the year of first publication, and the legal owner (e.g., © 2007 Joe Smith or Copyright 2007 Jane Jones).
Copyright notice generally should be provided regardless of whether the copyright has been registered.
Copyrights can be lost if a work is published without proper notice.