Call the surveyors, because these property lines don’t seem to be entirely accurate!
The borders work about as you’d expect, showing placement limits, though some objects can be clipped through or even be placed about one square grid outside of the limit before the indicator turns red. Other property lines are also visible to you while in Edit Mode, though they all disappear upon moving out of bounds or closing the menu manually. These borders are not yet present on live servers and should presumably arrive with the pre-patch next month.