Hello,
I agree the hat is wonderful. I love the color, is a pale chartreuse? I would date it to the mid to mid-late 1940s.
I cannot see the entire mark in the photo. From what is shown, I think it says "Berkshire". This is not the milliner's name or the name of the hat's designer. It is a trademark of the company that either made (or imported/purchased) the wool felt body, and probably also the line of hats that they (the parent company) marketed wholesale to the millinery trade. So it a maker's mark, but not the milliner's mark.
If can show the entire mark there is more information there too.
Thank you for sharing the hat with us, it is quite unusual with the circle trims.