Mystery Marking?

I hit all the likely places on the jeep looking for markings and here is what I found: uncovered the registration number on the right side (which confirms the "6" that I was unsure about):

The "S" is found at the end of the number, at the front of the jeep, not near the cowl where they say they are supposed to be:

Also uncovered a marking in white paint on the lower front cowl. It is present on both sides (on the driver's side it would be under the shovel if it were in place). Unfortunately, unlike the registration number, any amount of stripper that touched it almost immediately lifted it off. I had to stop working to remove any additional post-war paint for fear of destroying what was left of what seems to be a mystery marking. The left side of the marking has already been removed (along with all layers of paint) prior to my acquisition of the jeep. The yellow marking was applied by the civilian owner and was particularly resistant to my paint stripper. Here are two photos, one with flash and one without. Any ideas of what this is?