Army vs Navy Helmets
FYI, the Star on a wwii japanese flight helmet would indicate it was for an Army pilot. However, navy pilots did not use an "anchor" the navy symbol on their helmets.
Why exactly the army marked their helmets and the navy did not has to do with background and tradition. The japanese army was modeled after the german army while japan's navy was modeled after England's navy (both powers were scene as the top ranked militaires of their day, respectively).
The army was perceved more highly during the war; Tojo was an army general and the army was seen as an extension of the old
samurai class as this is most of the "old guard" when during the
meiji restoration. The navy was seen as second class in that they always received less funding, less draftees, etc. However, the navy airforce was a much more selective of its pilots and training standards was much higher (and so was the drop off rate, at least before the last years of the war).
Compared to the army, most of the pilots of the navy were from higher class families and in general, they held themselves to be better pilots than those of the army. They also had a tendency to purchase their own gear (made to mil specs). Helmets were also modeled after British helmets (the early type 30's are almost an exact replica) which had no visible insignia.
Army flight helmets were more standard with less variations. They appear to have been made to more exacting specs by military contractors since they were issued and not the private purchase ones made by taylor shops.
FYI, the attack at pearl harbor was by navy pilots, and the very first "kamikaze" corps were of navy pilots. Too often I see the japanese army pilot's helmets displayed in pearl harbor attack dioramas (for example, at the Pearl Harbor Memorial museum display in hawaii -I'm not kidding!). I guess this is because people more easily identify them as being japanese pilots.
Anyhow, navy pilot helmets are much rarer than their army counterparts. I collect them instead of the army because I find them more interesting. I originally began collecting them b/c I was interested in understanding what drove these pilots to crash their fighters, and I figured it would be easier than finding japanese-american (442nd 100th, mis) items. I could go on and on, but I hope this helps.