Japanese helmet question

[keith]

What does the S inside the diamond mean on the back inside of the helmet?
should all helmets have this? Out of my two display helmets, one has it and one doesn't.....thanks

[Jareth]

It's the trademark/logo for Kobe Seiko steel. One of the most common of many manufacturers of helmet shells.

[keith]

Thanks-so not all helmets obviously would have this mark, right?

[Jareth]

Correct. This is just the most commonly found mark.