If you want to change that setting just for this export job:
1) Go into File > Export to PDF. Click on options.
2) Select the item "Marks", and set Mode to "Off".
If you want to make a global change to your "Print - Medium Quality" setting:
1) Go into Edit > Output Styles. Select Print - Medium Quality. Click on "Edit".
2) Select the item "Marks", and set Mode to "Off".
Manuel S.
Technical Support Representative