Thanks for the comments. The crosses are actually transfers from Veni Vidi Vivci. They were left overs from some medievals shields I was painting. I painted the car in its main Fieldgrey colouring, then painted the white square background on the car , applied the transfer to this & then used the Fieldgrey to touch up ensuring the white square was the same dimensions as the balkan crosses.
I had intended putting larger crosses on but I actually quite like the small but promient markings on the large vehicle.