Pull the chin strap brackets away from the helmet wall and look there. Often a date or a manufacturers mark. Not always, one of mine has the manufacturer, the other has nothing. Sometimes there is a stamp on the rough side of the leather liner also.
Z stitching in the rear so likely a late war or post WWII issue but this isn't always accurate either. Z stitch started in 1944-45 I think but went to end of production in most examples.