Comment depends on what you mean by 'signing' (Score 1) 130
The question I have is what you mean by 'signing' a document.
If you mean that a piece of paper has been physically signed by someone and then scanned and an image retained, then you need a document imaging system.
If you mean to go paperless and can get people to fill out online forms, you can make the case that they are doing the electronic equivalent of signing when they log into the system with their own username and password AND they click on a given button (eg. "Submit" or "Apply Signature") and perhaps type in their initials into a small text field.
There are at least two ways you can handle online forms with Plone: PloneFormGen or custom content types via Archetypes. If you use custom content types, the History tab shows you changes to the content item (who, when), and if you have a workflow assigned to it, the workflow history is retained as well, showing when the item was transitioned to, say, the "signed" state and by whom. If you use PloneFormGen, simply include in the form two hidden and/or non-user-editable fields (datetime with default value the current date/time, and username with default value the currently logged in user).
