I never knew much about this particular issue until I went in the National Guard back in 1983, but there is such a thing as "SIGN DISCIPLINE" in the matrix of the military (along with all the OTHER sorts of discipline--- etc etc etc til you're SURE that there has GOT to be a God because only God could create "LATRINE LIGHT and SOUND and LITTER DISCIPLINE PROCEDURES for use in UNFRIENDLY TERRITORY."

Anywho, in the bowels of Army discipline procedure manuals there is not only one but many manuals telling you how to do what, signage-wise. One manual I looked up dealt with acceptable colors for use on night convoy work, and one combination was black with, and I'm trying to be accurate here of THOSE was