Signing a Rhino file - author

I remember that it was possible to sign the objects from a Rhino file so that it was possible to prove to be the author. But I can no more find this feature. Was it a plugin for Rhino4 or Rhino5 ?

Hi Alan - there was a watermark feature but this has been removed - it was not possible to make it reialble enough to be useful in real life.

-Pascal