Unlike restrictions on the federal trademark registration symbol ®, as soon as creative expression is reduced to tangible form copyright exists. Typically, you can mark you book, software, etc… with the copyright symbol, the year of publication, the claimant and “all rights reserved.” For example:
© 2020, Smith & Hopen, All Rights Reserved.
However, if you want to recover: (1) statutory damages; (2) court costs; and (3) attorney fees, you need to register within three (3) months of publication or before actual infringement. Otherwise, you will likely be arguing for “lost profits” which are difficult and costly to quantify in court.