The Liners option in the Display Options dialog, will toggle on or off the display of liners on the model. (Liners are indicated by thick coloured line segments along boundaries where they have been applied).
Tip
If you are having trouble seeing Liners on the model:
Liners may be easier to see if you turn the display of Boundaries off in the Display Options dialog.
If bolts are installed on the same segments as liners, you may also want to toggle the display of Bolts off in the Display Options dialog.
For maximum visibility, you can always turn off the display of contours in the Contour Options dialog, by setting the contour Mode to Off.