git-format-patch question

Hi,

A few questions about git-format-patch:

1. When is one supposed to use --signoff?  I gather the answer is
   project specific, but a statement of what's expected for git
   itself would probably help clarify things for me.

2. How should I add extra notes to an email generated using
   git-format-patch?  Is this in the docs somewhere that I missed?  Is
   there a recommended way to do this?

3. Is signoff broken? I get:

    $ git-format-patch --stdout --signoff master
    fatal: unrecognized argument: --signoff  

   When I pass -s instead of --signoff, I get output, but no patch and
   no signoff looking thing.  Without --signoff and without -s, I get
   reasonable looking output.

Thanks,

+ seth