I'm giving a handout out at an upcoming lecture. It contains unpublished data that will soon (within the next year anyway, if accepted) be published. I trust the people at the conference to respect my wishes. What's a polite footer to include at the bottom of the handout to these ends?
This is not a situation that calls for subtlety. I recommend adding large bold capital letters across the top of the first page:
PRELIMINARY VERSION — DO NOT CITE OR DISTRIBUTE
I would also include a footnote at the bottom of the title page indicating where the final version will be made available.
A footer is likely to be overlooked.
Put the statement that this is unpublished, preliminary results, in your abstract or so.
You might also mark it by overprinting with "Preliminary" by using e.g. LaTeX' draftwatermark package.