I looked up Austrian helmets and could not find it. That was a great idea. I would not have known a NATO connection...if any. I would hazard a guess based on the sticker that this is post WW2.
Maybe the harness is in backwards
Swiss Model 1971 Steel Helmet This model Swiss helmet was developed in 1971 but was not fully introduced to the Swiss army until 1979. Despite numerous claims this is not a Swiss paratrooper helmet.