It's a helmet of the type used by Civil Defense, in my opinion.
Generally they were white painted and had on front the Civil Defense decal, I think that with this coloration were intended for other uses, such as used by staff embarked on naval convoys.
I have seen those strap attachment points somewhere before
OldSteel is right. It is a Civil Defense Helmet. I have one identical to it. I'd throw up pictures but unfortunately it's in storage. But it is a Model 1917-A2 for Merchant Navy in the Atlantic but others used them. Mine has a Civil Defense Decal on the front and I think it was Medical if I remember correctly. Definitely WW2 era though.