Original Spezial Signierstift special marking crayons for glass and leather. Available in yellow or red. All are in good condition with a little storage wear.
If you have ever owned mint un-issued equipment your might recall seeing these crayons' handy work somewhere. I have an ammunition carrying frame in my collection which still has red and yellow marking lines visible on the webbing. These would be used to mark leather and glass specifically but I have seen them used on webbing and cloth as well as many other things.
These ones in particular came from an old store's dead inventory; they were using them to price items. They would simply write the price on the bottom of an item and it would be wiped away. It will wipe off of glass and any smooth surface fairly easily.
If you want your stuff to look truly like it would have then adding a few manufacturing markings might help. Could also be put in your map case as they would have been used to write on the clear plastic grid window of the map holder.
Each crayon measures about 4 1/4" long.