How to create crop marks

If you’re printing something that’s eventually to be reproduced in significant quantities, and bound, it’s conventional to print on paper larger than your target product, and to place “crop marks” outside the printed area. These crop marks are available to the production house, for lining up reproduction and trimming machines.

You can save yourself the (considerable) trouble of programming these marks for yourself by using the package crop, which has facilities to satisfy any conceivable production house. Users of the memoir class don’t need the package, since memoir has its own facilities for programming crop marks.