In the United States, the protection of copyright is afforded automatically to authors of original works. You don't need to place a copyright notice, but it is desirable as protection against a defence of innocent infringement.
The format of copyright notices for visual works is governed by 17 U.S.C. § 401 :
(a) General Provisions.— Whenever a work protected under this title is published in the United States or elsewhere by authority of the copyright owner, a notice of copyright as provided by this section may be placed on publicly distributed copies from which the work can be visually perceived, either directly or with the aid of a machine or device.
(b) Form of Notice.— If a notice appears on the copies, it shall consist of the following three elements:
(1) the symbol © (the letter C in a circle), or the word “Copyright”, or the abbreviation “Copr.”; and
(2) the year of first publication of the work; in the case of compilations, or derivative works incorporating previously published material, the year date of first publication of the compilation or derivative work is sufficient. The year date may be omitted where a pictorial, graphic, or sculptural work, with accompanying text matter, if any, is reproduced in or on greeting cards, postcards, stationery, jewelry, dolls, toys, or any useful articles; and
(3) the name of the owner of copyright in the work, or an abbreviation by which the name can be recognized, or a generally known alternative designation of the owner.
(c) Position of Notice.— The notice shall be affixed to the copies in such manner and location as to give reasonable notice of the claim of copyright. The Register of Copyrights shall prescribe by regulation, as examples, specific methods of affixation and positions of the notice on various types of works that will satisfy this requirement, but these specifications shall not be considered exhaustive.
(d) Evidentiary Weight of Notice.— If a notice of copyright in the form and position specified by this section appears on the published copy or copies to which a defendant in a copyright infringement suit had access, then no weight shall be given to such a defendant’s interposition of a defense based on innocent infringement in mitigation of actual or statutory damages, except as provided in the last sentence of section 504 (c)(2).
You'll notice that the wording of the law is broad, except that it gives the Register of Copyright the power to prescribe positioning of notice.
A notice that falsely claims a later first publication year does not extend the term of copyright protection — if you first published an article on your website in 2010, a copyright notice that states 2015 does not extend the protection.
- You don't need a copyright notice at all, but it's helpful
- You can put a later year on the notice, but this doesn't protect it for longer
- Each of your examples would have the same effect. As pointed out, they don't designate an author. For some reason, I had mentally inserted them. However, for works published after March 1, 1989, copyright protection is automatic and no corrective steps are required. This may mean that a defence of innocent infringement may succeed.
Oh, and also - All rights reserved has a different meaning, essentially addressed in the question What is the effect of saying "we reserve our (client's) rights" when writing to another party to a dispute?