Unknown vietnam helmet marking HELP

So i got this vietnam helmet at my local flea market for $20.00 and ive never been able to figure out this mrking on the front and on the liner maybe one of you know? On the metal the bars are yellow with a black backround and on the liner im guessing they didnt have yellow or black so the bars are white. Let me know

I think you might have to resize your pics a little smaller so they fit in the window...it takes a few times to get used to posting pics on this forums setup!..mike

yes i did notice only on this picture that it is like this but it shows the marking up close thats prob why its so big. Sorry about this hope someone knows what this is as ive been looking for around a year nd still dont know