Horizontal rulers appear much more frequently than vertical rulers. But vertical rulers appear at times, and here are some examples. DWF London 2017 [pg. 4] places vertical rulers between key statistics But it is unlikely that these rulers help readers understand or identify the statistics.
King Wood AustraliaDirs 2015 [pg. 3] wads in very thick vertical rulers.
Allen Matkins CommlRE 2018 [pg. 16] covers four varieties of commercial space and names them in the margin, placing a vertical divider between each of them.
CMSNabarro UKRE 2016 [pg. 2] inserts not only vertical rulers between the four columns but also a horizontal ruler under “The UK picture”.
Taft Stettinius Entrep 2018 [pg. 4] eschews the horizontal look in favor of a vertical bar, in black. The bar is less a vertical ruler than a highlighter or a design element as it extends slightly above the material it sets off and not quite as far as the bottom of the material. Vertical rulers typically have something on each side, but this element has nothing on the left.