If your work is valuable then full protection can only be provided by completing both steps - affixing the copyright notice and registration. Three significant elements of copyright ownership must be understood in managing copyright ownership and registration. Selling the copyright - Copyright material can be bought and sold as can other property. Each of these elements can be sold or bought individually or as a group. Limitations on the exclusivity of these transfers of ownership are common in Silicon Valley.
Exclusive licenses exist when the right licensed can only be exercised by the licensee.
Transfers of copyright ownership can and should be registered with the Copyright Office for full protection. Basic copyright protection is provided by the U.S. Constitution. International agreements, such a the Berne Convention, extend U.S. copyright protection to over 100 countries world wide. Software piracy is widespread in Asia and is particularly difficult to enforce in countries such as China. Remedies are readily available within the U.S. and Berne Convention countries for copyright infringement.