You don't! Page 1 Para 1 of the looking Ally Handbook:
Hoods on smocks and combat jackets are never to be used. They can be either
a) Rolled up neatly or
b) Left unrolled for the messy look.
The hood serves no purpose, it is only there to make your smock look different. Any use of the use of the hood not already mentioned above and any other infringements of this rule are punishable under AGAI 67.
I reckon it's so the contractor making the things knows where to put the flag so it doesn't look as daft as putting it on the front side of the sleeve like they did a couple of years thus making a tidy profit for tailors when we all had to change them to match the crease!
smart procument ini't
somebody figured out if they told the contractor to leave the avalanche thingy pocket off that would be classed as a redesign so cost squillions but if they just asked for several thousand smocks in this seasons colours no extra cash