Vietnam Era helmet with 1 red stripe?

Hi all, I'm new to collectible military items but I wanted to start a collection to pass along to my son as he gets older. I picked up my first piece today, an M1 helmet. I believe it's post Wwii based on the newer style chin strap. Anybody have any idea what the single red stripe on the back means? Anybody got any other details on this helmet? I paid $30 for it at an auction. Did I do alright? Any idea of value (although I'm less interested in the value than just learning as much as I can about it). Thanks! Attachment 2898 Attachment 2899 Attachment 2900