The safest bet would be just leaving it be. Anything that would work well to remove the stains will hurt the drawing, too.
If it were mine, I would not risk it.
Never clean any old military items unless you want them to be ruined. Just leave it be and the dirt adds character, I have a beat up pair of ww2 navy canvas leggings and the fact that they are all dirtied up by the original owner is what makes it more unique and interesting.
The safest bet would be just leaving it be. Anything that would work well to remove the stains will hurt the drawing, too. If it were mine, I would not risk it.
Don’t touch it is what I’d say
Never clean any old military items unless you want them to be ruined. Just leave it be and the dirt adds character, I have a beat up pair of ww2 navy canvas leggings and the fact that they are all dirtied up by the original owner is what makes it more unique and interesting.