There are two ways to turn them off:
1) Multiple select the work features (center marks and centerlines) on your
view > Right Mouse Click > and uncheck the visibility check box.
2) Expand the browser to display the contents of each part / assembly and
perform an individual or multiple selection of each work feature > RMB >
uncheck visibility.
Once the visibility is turned off by either of the above methods the node in
the browser goes Grey.