When you prepare a document for print production, a number of marks are needed to help the print service provider align separation films for producing proofs, measure film for correct calibration and ink density, trim film to size, and so on. Printer marks indicate the boundaries of document boxes supported by Adobe PDF, such as trim boxes and bleed boxes.
You can add printer marks temporarily at print time using the Marks And Bleeds panel of the Advanced Print Setup dialog box, or you can embed printer marks in the file (and optionally in a layer) using the Add Printer Marks dialog box. For information about adding printer marks to just the printed output, see Include marks and bleeds.