You are only required to do it however you have defined in your procedure for document control.
Someone correct me if I'm wrong, but I don't think that AS9100 prescribes a "marking" of documents by way of stamp, or even that you need to have hard copies (because electronic methods work just as well for some), but rather it allows you to define the controls yourself, hence the requirement for a document control procedure...
Once you have done that, you can identify and control your distribution however you wish, as long as it is effective in adhering to the controls you have established in your procedure.
So get creative with it...your intuition will follow your creativity.
Hope I've helped...

Brian