Tom Hanks has captain's bars on his combat helment, this is a major no-no! He would be the first person shot by an opposing German sniper or regular soldier, by "advertising" his rank!
Don't soldiers have their rank indicated on their sleeve as well? If that is the case (which I'm pretty sure it is) then what's the difference if he has it on his hat too?
Officers didn't ware rank on their sleeves, they wore it on their collar, and a Ranger should know quite well not to wear shiny rank, its just too bad they didn't have subdued rank back in those days. Back then, though, they still did wear rank out on the field, as to this day, just now they subdue it so it doesn't stand out.
Actually, officers did receive helmets with their rank on them, as in combat, it was pretty tough trying to see rank on the epaulets or collar.
Officers are always going to be more conspicuous. Just how it is.
The officer rank markings on the helmets were put there for recognition by the landing troops during the confusion of the landings. Officers and NCO's needed to be instantly recognized by the men. NCO's had a horizontal thick stripe on the back of their helmets, officers had a vertical stripe on back, plus rank on front. The theory here being that the enlisted men, through the haze of battle, could zone in on the white helmet markings and naturally follow the owner. The fact that a German or Japanese sniper could zone on it too, was an unfortunate consequence. The powers that be felt that recognition by your own troops took higher precedence than the Officer or NCO's immediate safety. If the men didn't follow these Officers and NCOs off the beach, then the invasion would fail. Period! The painted helmets served their purpose on that beach. Later in the Normandy campaign, and for the rest of the war, Officers tended to paint over their helmet rank insignia ( as well as pulling insignia off jackets ) as a matter of personal preservation, Army regulations be damned. Since the casualty rates for company grade officers was so high, the Army didn't enforce the policy. Combat experienced officers were too hard to replace.
Here is a photo showing the rank bars on helmets:
http://history.amedd.army.mil/booksdocs/wwii/medicalsupply/ch10fig75.jpg
("Medical care on Omaha Beach, June 1944"
- the captain in the middle of the picture clearly has bars on his helmet