Hats

I've got the most hats, therefore I am commissar.

In the grim darkness of the far future, the size of your hat determines how important you are. If your hat appears to be larger than those around you, you may be an important person!
You do still have to kiss the ass of anyone with pauldrons, but whatchagonnado?
Consult your local imperial administration office for further instructions if you believe you have a large hat.

Note that if your hat has frills, you may instead be a little girl. Should this be the case, instead contact your local shrine maiden.

Also, notice that helmets are not a form of hat, in fact, they are quite the opposite. While a Hat makes you more important, a helmet makes you less important. This can be seen in the "trooper-sergeant" relationship: The basic troopers have a helmet, and are less important than the sergeant, who seems to invariably go without any kind of helmet or hat. This shows a clear social heirarchy in head and shoulderwear:
Helmet < No helmet < Hat < Pauldron + Helmet < Just Pauldron < Pauldron + Hat
Hell, even Tyranids wear hats. And, of course, the Hive Tyrant has the biggest hat of all, therefore is leader.

Take note that no-one has ever been seen as so important as to have Pauldrons AND a Hat, not even the Empra.

Few people know that were GW to actually move the turgid plot of 40k along, it would be revealed all the races are in fact fighting for a cargo ship full of hats.