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 It contains unpublished data that will soon (within the next year anyway, if accepted) be published.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PRELIMINARY VERSION — DO NOT CITE OR DISTRIBUTE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.