Hm, maybe it was a marine? We know they like their crayola! Aside from the joke, try doing a little spot cleaning on the stripes or something with goof off, and I mean an extremely small amount on something like a q-tip. I'd even try an eraser if you think it's crayon, but I think you might want to just try wiping it off with water.
And I will say the oil stained paint makes me think that what ever was used was of course, oil based.
Thank you for reply !
I was just about to post the effect of my yesterday's work.
I was afraid that Goof-Off can take off the base paint too, so after few attempts with baking soda.. eraser and heat gun.... the only product that was dissolving this crayon was WD40 !
Yet because WD40 was leaving dark greasier spots after cleaning - I had to spray whole top of the helmet to make even colored surface. then I picked up as much of WD with paper towels and I left it in the sun to bake and evaporate the rest.
Some folks asked if I am really sure it wasnt trench art... well I have never seen crayon trench art, and this greasy border around the skull was also pretty clean without any dust/dirt deposits so i think it was done recently
this helmet is signed to a Sgt. in 157th Infantry of 45th National Guard Division and dated 1927