The GWR Roundel or Shirtbutton monogram was used on GWR locos and rolling stock during the period 1934-1942. On locos it was in gilt with a black outline, positioned in the center of the tank or tender sides. Unfortunately it was so small as to be insignificant in these locations, often disappearing entirely when wheathering set in.

On coaches, the monogram was carried in the center below the waist, while "brown" vehicles and containers carried the monogram in various locations on the sides. The monogram looked considerably better on the brown stock, where it was applied in yellow. Ordinary grey goods vehicles never carried the monogram, retaining the letters "GW".