In order to exclude documents from the signature wizard, the first step is to open up the form template that you want excluded.
Other > System Administration > Form Templates then choose the document or create a new one.
Once you have the document open, there is a setting in the form on the right hand side:
Check that box and you're all set.
Reviewing your settings
As always, to quickly review what settings and requirements are attached to each form in your library you can navigate to the chart info page from Other > System Administration > Form Templates
That's it. You're done.