you can see them in a few images on various vehicles during Op DS.
And the 43 ambulance in the background.
I would just cut some plain white tissue paper and then coat it with a 50/50 layering of white PVA glue and water and brush it over until its soaked and let it dry. when its close to fully drying, you can shape it how you want over the rear back bin and then paint it yellow/faded yellow etc.
His in the pic you posted looks very new and full on bight yellow … the ones I posted look a lot older and faded.