Print with a black border to show page "edge"?

I'm printing a letter size document from illustrator at 50% size. All pages have a white background so I would like to have the document print with a black rule/ border around it so I can tell what it will look like. Is there a way to do this without manually putting a rule around all 25 existing artboards? Or is there a way to do this in the Acrobat pdf I'm outputting from this doc?(CS5) - many thanks!

You can print with crop marks very easily and that will give you the general idea of how it will crop with almost no work. In Illustrators print settings, go to Crops and bleeds and click on trim marks.