Adding a sheet marks file to the output process template should be done with great care. Before placing a sheet mark, you must know:

Do not position sheet marks under the plate clamps. If you position the sheet mark under the clamps, some or all of the sheet mark will not be imaged.
Sheet marks are set to overprint. If you position the sheet mark over an object, the sheet mark will overprint the object.
Use the Virtual Proofing System software to check the sheet mark placement.