The official documentation is at: http://docs.alfresco.com
Company CEDITI created an Electronic Signatures module for Alfresco.
With this module, end-users are able to digitally sign a document very easily, directly from the Alfresco web UI.
Digital signatures can be used in the context of an Alfresco workflow, or as a simple action.
The implementation is based on standard certificate technologies for optimal security, and gives legal value to your documents.
See a presentation and a demo movie of the module on our website (in English)