Above Fig. 2.1 shows a small layout of road under development represented by 3D Polyline.
Below Fig 2.2 shows Labeling the 3D polyline with its elevation by choosing "Elevation" under What to label and choosing "At picked point" under Text spacing.
Below Fig 2.3 shows Labeling the 3D polyline with user string repeatedly at specified intervals by choosing "User String" under What to label and choosing "Repeated" under Text spacing and specifying the text to repeat in the Label String box under Other Annotation parameters.
Above Fig 2.3 shows the 3D polyline labeled with User specified String and repeated at specified interval.