I have a WWI Helmet that was supposedly my great-grandfathers, he served with the Americans in 1918 over in Europe and received a Purple Heart in 1966 by the Johnson Administration commemorating his service, but his helmet is a basic Brodie Helmet but it has a decent sized red blob in the helmet, could this represent his regiment or something?
The red blob may be a misshapen and/or discolored symbol showing regimen, status, or possibly achievement/rank based on the location of it. It could also be an injury stain?
