This article is from the Copyright Law FAQ, by Terry Carroll with numerous contributions by others.
As noted in section 2.3, under U.S. law, a work is copyrighted as soon as
it is created. No notice is required to retain copyright. While most of
the world has operated this way for some time, this is a comparatively
recent change in U.S. copyright law, as of March 1, 1988, the effective
date of the Berne Convention Implementation Act, PL 100-568, 102 Stat.
2853 (See sections 4.1 and 4.2 for a discussion of the Berne Convention).
Although notice is no longer a requirement, there are still some sound
reasons for using one anyway.
If you include a copyright notice on a published copy of your work to
which the defendant in an infringement suit had access, he or she may not
plead "innocent infringement" (i.e., that he or she was not aware and had
no reason to believe that his or her acts constituted infringement, the
so-called "innocent infringement" defense) in mitigation of actual or
statutory damages. 17 U.S.C. 401(d), 402(d).
Unlike the decision of whether to register your work, this is a no-
brainer, since it's simple and free: just include a notice on every
published copy of the work.
A proper copyright notice consists of three things: 1) the letter "C" in
a circle (called, logically enough, the "copyright symbol"), or the word
"Copyright," or the abbreviation "Copr."; 2) the year of first
publication; 3) the name of the copyright owner. 17 U.S.C. 401(b).
Using "(C)" in place of a copyright symbol is not a good idea. To the
best of my knowledge, no court has expressly ruled one way or another
whether "(C)" is a sufficient substitute for a copyright symbol. One
case, Videotronics v. Bend Electronics, 586 F.Supp. 478, 481 (D. Nev.
1984), implies that it is not sufficient; another, Forry v. Neundorfer,
837 F.2d 259, 266 (6th Cir., 1988), implies that it might be. While
courts are generally lenient in allowing for what makes up a valid
notice, it's best to be squarely within the statute. If you can't make a
copyright symbol, either spell the word out, or use the "Copr."
As a side note with regard to international protection, the Universal
Copyright Convention requires that, at a minimum, all signatory nations
that require notice must accept the C-in-a-circle variant; it does not
provide a provision for a spelled out variant. On the other hand, most
nations that have signed a copyright treaty are signatories to the Berne
Convention, which forbids requiring a notice as a condition to copyright.
See section 4.1 for details.
For a sound recording, the notice requirement is similar, except that it
uses the letter "P" (for "Phonorecord") in a circle, plus the year and
owner name. 17 U.S.C. 402(b). The statute does not provide a spelled
out alternative to the P-in-a-circle.