Authors do not have to sign over copyright to publish. The only copyright that publishers need - is permission to publish!
The Scholarly Publishing and Research Coalition (SPARC) has made available an Author's Addendum, to be attached to any author copyright transfer form, clarifying that the author is retaining their rights, for example for self-archiving purposes.
The Author's Addendum, and related resources such as the Author's Rights brochures, can be found on the SPARC Author's Rights page.
This post reflects my personal opinion only and does not represent the opinions or policy of the BC Electronic Library Network or the Simon Fraser University Library.