Marking your work with a copyright notice does a number of things:
– notifies the public that the work is protected by copyright and that the owner takes that protection seriously
– distinguishes the work as not being in the public domain (although absence of © doesn’t mean it is public domain)
– identifies you as the owner
– shows the year of the creation of the work and any subsequent updates
– prevents a copier from claiming ignorance of protection over the work
What should your copyright notice actually say? It should identify the owner, the date the work was created, the date it was revised (if any). And of course, it should say something like “Copyright,” “©,” or “Copr.” Sometimes you will see “All rights reserved.” This isn’t really necessary, but it doesn’t hurt to add. Maybe it will make you feel more official.